Step 1: Understanding the concept.
This is a question tag, which is a short question added to the end of a statement for confirmation. The rule is that if the main sentence is positive, the tag must be negative.
Step 2: Grammar rule for question tags.
Structure: Auxiliary verb + subject (pronoun)
If the main clause uses “will,” the tag uses “won’t.”
Step 3: Analyze the sentence.
The statement “They will wash the car” is positive. Hence, the tag should be negative → “won’t they?”
Step 4: Analyze the options.
- (a) will it: Wrong; subject mismatch (should be “they”).
- (b) won’t they: Correct; matches subject and verb polarity.
- (c) wouldn’t they: Incorrect tense.
- (d) couldn’t they: Incorrect auxiliary verb.
Step 5: Constructing the complete sentence.
“They will wash the car, won’t they?”
Step 6: Conclusion.
Thus, the correct question tag is “won’t they.”