Four bodies oscillate along the OY axis, the dependence of the coordinates on time is expressed by the formulas:
1) y=y0sinωt, 2) y= y0cosωt, 3) y= y0cos2ωt, 4) y = y0sin2ωt.

In what case are the vibrations harmonic?
1) 1, 2, 3 and 4; 2) 1 and 4; 3) 1 and 2; 4) 2 and 3.