[单选题]
A jumper in the long-jump go beaklevf f 2cj/):g.6 fp;g969 :eyd3-as 7cf9mp (b/;ls oqi leiivdes into the jump with a speed of 12 m/s at an angle 6s:lg(3i 9; 7ebdvmie9 c li;fa9fspo -pd/yqof $20^{\circ}$ 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. $1.3 \; s$
