Ball a moves horizontally. According to the displacement formula, there are:

x=v 1t…①

y = 12gt 2……②

And tan 30 = yx...③

Simultaneous: v1= 32gt ... ④

If the ball B hits the inclined plane vertically, there are: tan 30 = V2vy = V2GT … ⑤.

So: v2 = 33gt……⑥ ... ⑥

From 46: v1:v2 = 3: 2.

So choose: C.