According to the frequency step histogram, a =1-0.05-0.1-0.2-0.35 = 0.3.

The number of students whose height is [120, 130], [130, 140], [140, 150] are respectively

0.3×200=60,0.2×200=40,0. 1×200=20

There are 60+40+20= 120 in three groups.

Stratified sampling selection 12 people to participate in an activity.

The probability of each individual being drawn is12120 =110.

∴ The number of students whose height is less than [130, 150] should be 1 10×60=6.

So choose B.