Dots and __
elongate rhythm.

A. rests
B. triads
C. ties
D. res

C. ties

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.

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