Question

Which sentence contains a restrictive clause?

The road, which was long and winding, took us deeper and deeper into the dark forest.
The parrot, which must have been tame, flew out of the tree and landed on my shoulder.
Aware that I could be bitten, I carefully approached the trapped dog, which growled at me.
The astronaut who first stepped on the moon was Neil Armstrong.

Answer 1

"The astronaut who first stepped on the moon was Neil Armstrong."

Explanation: "who first stepped on the moon" is a restrictive (essential) clause — it identifies which astronaut. The other sentences use clauses set off by commas (nonrestrictive), which add extra information.