Identify the sentence that has a problem in subject-verb agreement.
a. the sales tax increase, although not favored by some business owners, was overwhelmingly voted in by the legislature.
b. the most dedicated volunteers at our local homeless shelter were once homeless themselves.
c. handheld devices, including cell phones and tablets, are rapidly replacing personal computers for many users.
d. many musicians, including unlikely candidates such as elvis presley, has been influenced by gospel music.