B. he explained how learning different verbs helped him, which is a specific example.
Answer:
You're picked up by your son.
Explanation:
The following sentence contains an adverb clause.
This sentence contains two clauses - an independent clause (We moved) and a dependent/subordinate clause (because our house was too small). Given that the second sentence gives us a reason why they moved, it acts as an adverb, which is why it is an adverbial clause.
