Choose the appropriate option to fill in the blank :

The doctor advised that I ________ strictly follow the diet plan.

should

The correct option to fill in the blank is should.

The modal verb should is used to express advice or recommendation. In the sentence "The doctor advised that I strictly follow the diet plan," the doctor is giving advice to the patient to follow the diet plan.

The other three options are not as appropriate:

• Will is used to express future certainty.
• Can is used to express ability or permission.
• Might is used to express possibility or uncertainty.