[单选题]
A radar receiver indicates the: fye6 -riu n83dg5pwat a tran6, gt(w6/pq fazjl 0lasmitted pulse return as an echo in 20 ms after transmission. How far aww 0z/6a,ptag l(6lfq jay is the reflecting object?
A. $1.5 \; km$
B. $3.0 \; km$
C. $6.0 \; km$
D. $9.0 \; km$
