B
1) Since it is a reflection across the y-axis we can write the following rule:
Pre-image Image
(x, y) (-x,y)
2) Plugging the vertices of ABC we have
Pre-image Image
(x, y) (-x,y)
A(-3,4) A' (3,4)
B(0,2) B' (0, 2)
C(-2,1) C' (2,1)
3) Examining the options, the answer is B