Select the most appropriate option that can substitute the highlighted segment in the given sentence. If there is no need to substitute it, select ‘No substitution’.
Unless he has permission from his parents, he wouldn't travel alone.

Correct option is D

The correct substitution of the highlighted words is "Unless he had permission from his parents."
The original sentence "Unless he has permission from his parents, he wouldn't travel alone" uses a mixed conditional incorrectly by combining "has" (present tense) with "wouldn't" (conditional perfect).
· The correct form should match the tense in the conditional clause with the result clause. Using "had" (past simple) with "wouldn't" (conditional perfect) forms a correct second conditional structure, which is used to talk about hypothetical situations.
· Grammatical rule used: In conditional sentences, particularly the second conditional, the if-clause typically uses the past simple tense, and the main clause uses the conditional perfect.
· Example: Unless he had permission from his parents, he wouldn't be allowed to travel alone.