Hello!
The answer is:
d) volvieron (they came back)
Why?
We are given a Spanish sentence which refers to some people that came back early, so, we need to find which of the given options can fit with the sentence.
We have the sentence:
Ellos____ temprano.
They_____ early.
Since the sentence is referring to the second-person plural (ellos), we can see that the only option that fits with the sentence is volvieron (they came back).
Hence, the correct option is d. "volvieron" or "they came back".
The sentence will be:
Ellos volvieron temprano.
They came back early.
Have a nice day!