[单选题]
A radar receiver indicac1fu;7aohwa19r a f t8t7tile l*l4 8hdit mn)6h)h m4ees that a transmitted pulse return as an echo in 20 ms after transmission. How 8lhm64)ehitn*t4 h l 7ilme)dfar away is the reflecting object?
A. $1.5 \; km$
B. $3.0 \; km$
C. $6.0 \; km$
D. $9.0 \; km$
