Which sentence contains an incorrect possessive form?

a. his solution took everybody's objections into account.

b. the credit for the decorations is all hers'.

c. it looks as though that calf has wandered away from its mother.

d. someone's bike is in the driveway.

B. The credit for the decorations is all hers'.

Explanation:

Hers does not require the apostrophe.  It is a possessive pronoun, and they are used without the apostrophe.    

Answer choices A, C, and D are good.  

- "when these words are put together to convey a meaning it is known as a sentence. a sentence is a group of words that makes complete sense. placing of words in a sentence is very important. the second sentence is a question."