C
you don't need to know how I know.
If the "books" wasn't a plural, it would be "his" but since it isn't singular, it would be "their"
I really dont know lol........
1. The truck tumbled down the street rapidly.
2. The man drudged home from a day of work sadly.
It said I could add my own choice of adjectives or adverbs after the sentences and so, I did just that. I hope this helps!
