[单选题]
A radar receiver indiffbt,qd8ueenp6 12pr l p9 r12cate-8- q4 rn.moe baw4jvss that a transmitted pulse return as an echo in 20 ms after transmission. jbwr.ov4 senm4 - a-8q How far away is the reflecting object?
A. $1.5 \; km$
B. $3.0 \; km$
C. $6.0 \; km$
D. $9.0 \; km$
