[单选题]
A radar receiver indicatesx5tsb33a)gshw3 )w t d that a transmitted pulse retykjnn6(q9w/axjz) i-urn as an echo in 20 ms after transmiswx)(yk6 zai9/n n-jjq sion. How far away is the reflecting object?
A. $1.5 \; km$
B. $3.0 \; km$
C. $6.0 \; km$
D. $9.0 \; km$
