Margaret forgot to buy … — choose the word or group of words that best completes each of the following…

Analyze the question: The sentence is "Margaret forgot to buy __." We need the option that is grammatically correct with the noun trousers.

Explain the concept: Some nouns name items made of two joined parts, so they are always plural in form. Examples are trousers, scissors, pliers, spectacles, shorts, pants. Because they are plural in form:

• You cannot use "a" or "one" directly before them (so a trousers and one trousers are wrong).
• To talk about a single item, use the phrase "a pair of" (a pair of trousers, a pair of scissors).
• "Plenty" is used with plural nouns in informal speech, but "plenty trousers" is wrong. You would need "plenty of trousers".

Step-by-step solution:

• A. a trousers: wrong, because "a" is singular and "trousers" is plural in form.
• B. one trousers: wrong, for the same reason.
• C. a pair of trousers: correct. "A pair" is singular and refers to the single item, and "trousers" follows "of" correctly.
• D. plenty trousers: wrong, because it needs "of" (plenty of trousers). It also does not fit naturally here.

Answer: The correct option is C. a pair of trousers.

Tip: For any "two-legged" or "two-bladed" item (trousers, scissors, shorts, glasses, pliers), remember the phrase "a pair of" when you mean one. WAEC often tests this.