What is tempo=c.120?

i want to know what is (c.),what it means?

It means circa, or around, so the tempo should be around 120 beats per minute.

maybe it means crotchet =120. You can check the metronome to find the right tempo.

I think (c) means common, so the song commonly played at 120 tempo.

c is for circa simply meaning 'about'
'Crotchet=c.120' means about 2 crotchet beats per second!

It means 120 beats per minute (ie 2 per second). This speed is approximately that of a quick march.