The law says that all public buildings must be accessible to people who have trouble _____. A. walki

The law says that all public buildings must be accessible to people who have trouble _____. A. walking B. walk C. to walk D. walked

The correct answer is A. walking.

In this sentence, the phrase "have trouble" requires a gerund (verb form ending in -ing) to follow it. The structure "have trouble + gerund" is grammatically standard in English, where the gerund functions as the object of the phrase.

"Walking" (A) is the gerund form of the verb "walk" and fits perfectly in this structure.

"Walk" (B) is the base verb form and cannot follow "have trouble."

"To walk" (C) is the infinitive form, which is grammatically incorrect in this context.

"Walked" (D) is the past participle form and does not fit the grammatical structure required here.

This rule applies to similar phrases like "have difficulty," "avoid," and "enjoy," which all require gerund forms. Why do you think English developed this specific grammatical pattern for these verbs?