Pronoun : - A pronoun is used in the place of a noun. It substitutes the noun in a paragraph or piece of writing to avoid repetition of the noun. Pronouns can be used in singular and plural forms.They usually refer back to a noun used earlier in the sentence, and they must match the number, point of view, and gender of the noun.

Relative Pronoun: - are words that add information about a noun or tell the relationship between different things. A relative pronoun is a word, such as : who, whom, that or which that is used to introduce a relative clause. These words are called relative pronouns. The compounds whoever, whomever and whichever are also relative pronouns.

In other words, A pronoun which is used to begin a subordinate clause can be referred to as a relative pronoun, since it indicates the relationship of thee subordinate clause to the rest of the sentence. A subordinate clause which is introduced by a relative pronoun is often referred to as a relative clause .

Example : - The woman, who is wearing red saree, is a doctor. Here , who is a relative pronoun as it refers to the noun woman .

In the question : -

1. The teacher appreciated the student who solved the math problem. In this sentence , who is the correct relative pronoun as it refers to the noun student

2. I love the ukulele that my aunt bought me. In this sentence , that is the correct relative pronoun as it refers in a defining clause that refers to a person, animal or thing .

3. Teena did not return the white bag that she borrowed. In this sentence , that is the correct relative pronoun as it refers in a defining clause that refers to a person, animal or thing .

Thus , the Correct Option is B  , which is who , that , that .

Pronoun : - any of a small set of words (such as I, she, he, you, it, we, or they) in a language that are used as substitutes for nouns or noun phrases and whose referents are named or understood in the context.

Relative Pronoun: - are words that add information about a noun or tell the relationship between different things. A relative pronoun is a word, such as : who, whom, that or which that is used to introduce a relative clause. These words are called relative pronouns. The compounds whoever, whomever and whichever are also relative pronouns.

In other words, A pronoun which is used to begin a subordinate clause can be referred to as a relative pronoun, since it indicates the relationship of thee subordinate clause to the rest of the sentence. A subordinate clause which is introduced by a relative pronoun is often referred to as a relative clause .

Example : - Paneer pasanda , which we eat at least twice a week, is one of my family's favorite meals. Here , which is a relative pronoun as it is used in a non-defining clause that refers to a person, animal or thing .

In the question : -

The person ________ stayed with me last night was my best friend. In this sentence , who is the correct relative pronoun as it refers to a person .

Thus , the Correct Option is D , which is who.

Pronoun : - A pronoun is a word that you use to refer to someone or something when you do not need to use a noun, often because the person or thing has been mentioned earlier. Examples are 'it', 'she', 'something', and 'myself'. '

Relative Pronoun: - are words that add information about a noun or tell the relationship between different things. A relative pronoun is a word, such as : who, whom, that or which that is used to introduce a relative clause. These words are called relative pronouns. The compounds whoever, whomever and whichever are also relative pronouns.

In other words, A pronoun which is used to begin a subordinate clause can be referred to as a relative pronoun, since it indicates the relationship of thee subordinate clause to the rest of the sentence. A subordinate clause which is introduced by a relative pronoun is often referred to as a relative clause.

Example : - The woman, who is wearing red saree, is a doctor. Here , who is a relative pronoun as it is used to introduce a relative clause .

In the question : -

The door, which is dark blue, is very tight. In this sentence , which is a relative pronoun as it is used to show the relation of door with remaining part in the sentence .

Thus , the Correct Option is C , that is which .