Answer:
C. ties
Step-by-step explanation:
A tie is that little smiley face line drawn between two notes of the same pitch. If you want to play a C for two beats, but it's over the barline, connect them with a tie.
Similarly, a dot adds half a note's value to a note. For example, a dotted quarter note gets 1 and a half beats.
This is all elongation, or extending a rhythm, as opposed to making it shorter.