[单选题]
A radar receiver indicates that a transmitted pulse return as an edx6uym./1n kn phw5p, 85ygpw, yngn8cho in 20 ms after transmission. How far away is th5y,8g wnp 8ngye reflecting object?
A. $1.5 \; km$
B. $3.0 \; km$
C. $6.0 \; km$
D. $9.0 \; km$
