Mary did her best … failed to reach the pass mark

Analyze the question

The sentence is "Mary did her best ..... failed to reach the pass mark." We need a word that correctly joins the two parts. The first part says she tried hard, and the second says she did not succeed. These ideas contrast.

Explain the concept

A coordinating conjunction joins two clauses of equal rank. The common ones are for, and, nor, but, or, yet, so (FANBOYS).

• but shows contrast, meaning the second idea is unexpected given the first.
• and adds similar ideas.
• so shows result.
• however is a conjunctive adverb (a linking adverb). It cannot join two clauses with only a comma or no punctuation. It needs a semicolon before it and a comma after it, as in "Mary did her best; however, she failed to reach the pass mark."

Step-by-step solution

1. "Did her best" suggests success should follow, but "failed" says the opposite. We need a word of contrast.
2. This leaves but and however.
3. "Mary did her best however failed..." is ungrammatical, because however needs a semicolon and a comma, and the sentence has no punctuation to support it.
4. "Mary did her best but failed to reach the pass mark" is correct. The subject "Mary" is shared by both verbs (did and failed).
5. So wrongly implies that failing was the result of doing her best, and and does not show the contrast.

Correct answer: A. but

Exam tip: When a blank sits between two parts of a sentence with no punctuation, look for a coordinating conjunction such as but, and, or so. However usually needs a semicolon before it and a comma after it. Always check the meaning first (contrast, addition, or result), then check the grammar.