C. Incomplete sentance. Suboridinate clause.
The girl riding her bike is not enough to be a full sentance.
Some things you could do to fix it:
The girl was riding her bike.
The girl riding her bike was very pretty.
The girl was riding her new bike.
Correction!!! I read this over a few more times and I think it is the fourth one because it says "words that were once considered slang are now words of full, legitimate standing in our language." It's talking about the the past tense and present tense of slang. So sorry for the confusion
Exercise 9
1. Comp. subs:
Apples and oranges
Verb: are
2. Comp. subs:
Vitamin C and dietary fiber
Verb: are