Solution: This problem is mainly solved by equal flow, as shown in the following figure:

Q2 = S2 v2 = q 1-Q2 = s 1v 1-S3 v3；

v2=(s 1v 1-s3v3)/s2=v 1-(d3/d 1)v3= 1-( 100/200)^2*2=0.5(m^3/s)。

A: ......