Fill in the blank with a modal that expresses ability:
He ________ lift that heavy box.
 (a)Can
 (b)Might
 (c)Ought to
 (d)Must

Hint: Read the given sentence and see what it is trying to covey. Now go through the options and use the hit and trial method to check which of them helps the sentence to express itself the best.

Complete answer: A modal auxiliary is an auxiliary verb (such as `can' or `will') that is used to express modality. Modality refers to a classification of propositions on the basis of whether they claim necessity or possibility or impossibility.

In the given question, we have to find out which option expresses ability.
Let us analyze the options given to us in this question -
Option (a), 'can', refers to a modal that expresses ability, therefore, option (a.) is correct. For example – She can play the guitar.
Option (b), ‘might', refers to a modal (auxiliary) used to indicate conditional or possible actions. Therefore, option (b.) is incorrect as we need a modal that expresses ability.
Option (c), ‘ought to', refers to ‘(auxiliary) indicating duty or obligation’.
Therefore, option (c.) is incorrect as we need a modal that expresses ability.
Option (d), ‘must', refers to ‘(modal auxiliary, defective) to do with certainty; indicates that the speaker is certain that the subject will have executed the predicate’.
Therefore, option (d.) is incorrect as we need a modal that expresses ability.

Note: In this question, it will be helpful for the student to recall the concept of ability. Ability is the quality of being able to perform; a quality that permits or facilitates achievement or accomplishment; the possession of the qualities (especially mental qualities) required to do something or get something done. Subject: English