[单选题]
A jumper in the long-juj h/+y-bg 5tecmp g+8ax n +zy:isyoes into the jump with a speed of 12 m/s at an angle xy:z +ayn s8+iof $20^{\circ}$ above the horizontal. How long is the jumper in the air before returning to the Earth?
A. $0.21 \; s$
B. $0.42 \; s$
C. $0.84 \; s$
D. $1.3 \; s$