String A is denser and tighter than string B. As a result the waves in string A are

Answer: Faster OR slower! (Both b and c are correct answers here!)
Don't worry. There will be no more questions with two possible answers in my exams. I wanted to make you aware that from the first question onwards you should be alert. Nature is kind of tricky. Your common sense needs checking and rechecking, but in the end it works:

As uncle Albert (Einstein) used to say:
"The Lord God is Subtle, but Malicious he is not" (May, 1921)

From class demonstration & lab #1: When a string/slinky is stretched the waves move faster. Also, when the string/slinky is more massive the waves take longer to come back, so the waves go slower. The combination of the two will give
Either a slower wave OR a faster wave, depending on the change of mass density and tension.