My son () to run one mile in two minutes.

• A. Is able
• B. Can
• C. Could
• D. Might

Answer: (A)

Expressing ability in the present tense uses be + able to + verb. Here, the phrase that follows the blank is “to run,” so the blank must supply a form that combines with “to” to express capability. The correct choice is “is able,” giving the natural sentence: My son is able to run one mile in two minutes.

Why this fits: be + able to + base verb is the standard way to state ability when you want the infinitive to follow. The other options are modal forms (can, could, might) and don’t combine with “to” in this construction. If you used a modal, the sentence would normally need the infinitive without “to” (for example, “My son can run…”), which wouldn’t align with the given structure that has “to run” after the blank.