Modals: They are verbs which are used before the main verb to express ability, possibility, obligation, permission, suggestion, request, certainty or necessity.They indicate the attitude, intention and the mood of the speaker.

• They cannot be used alone in a sentence.
• In case of Questions they are used alone.
• They are not affected by the change in person i.e. first, second or third form.
• Present Participle or Past Participle form of a verb is never used with a modal.

Use of Should:

1. Should can be used to express duty, responsibility, advice, probability, expectation, presumption, moral obligation and mild command e.g.

   (a) One should obey ones elders. (duty)

2. Should is also used for expressing purpose like may and might. e.g.

In the question : -

1. This _________ be Mark’s house.

In this sentence , shouldn't is the correct modal that can be placed in the blank part as it is used to show probability / expectation .

2. You __________ go to the hospital tomorrow or you will be more sick.

In this sentence , should is the correct modal that can be placed in the blank part as it is used to show advice .

3. For going abroad, you ___________ go to a language course first, I am sure it will be very useful.

In this sentence , should is the correct modal that can be placed in the blank part as it is used to show advice or suggestion .

Thus , the Correct Option is C , which is shouldn't , should , should .

Modals: They are verbs which are used before the main verb to express ability, possibility, obligation, permission, suggestion, request, certainty or necessity.They indicate the attitude, intention and the mood of the speaker.

• They cannot be used alone in a sentence.
• In case of Questions they are used alone.
• They are not affected by the change in person i.e. first, second or third form.
• Present Participle or Past Participle form of a verb is never used with a modal.

Use of Should:

1. Should can be used to express duty, responsibility, advice, probability, expectation, presumption, moral obligation and mild command e.g.

   (a) One should obey ones elders. (duty)

2. Should is also used for expressing purpose like may and might. e.g.

In the question : -

1. I taught her so that she ___________ pass.

In this sentence , should is the correct modal that can be placed in the blank part as it is used for expressing purpose like may and might.

2. He _________ smoke. And he ________ stop drinking too.

In this sentence , should , should is the correct modal that can be placed in the blank part as it is used for offering advice or opinions (similar to ought to) .

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

Modals: They are verbs which are used before the main verb to express ability, possibility, obligation, permission, suggestion, request, certainity or necessity.They indicate the attitude, intension and the mood of the speaker.

• They cannot be used alone in a sentence.
• In case of Questions they are used alone.
• They are not affectefd by the change in person i.e. first, second or third form.
• Present Participle or Past Participle form of a verb is never used with a modal.

Use of Should:

1. Should can be used to express duty, responsibility, advice, probability, expectation, presumption, moral obligation and mild commang e.g.

   (a) One should obey ones elders. (duty)

2. Should is also used for expressing purpose like may and might. e.g.

In the question : -

1. One ________ obey ones elders.

In this sentence , should is the correct modal that can be placed in the blank part as it is used to show duty .

2. Move fast lest you ________ miss the bus.

In this sentence , should is the correct modal that can be placed in the blank part as it is used to show  conditional sentences ( Lest means in case or so that ....not)

Thus , the Correct Option is B , which is should , should .