[单选题]
A radar receiver indi qndby2 ,y akej70b9-zcates that a transmitted pulse return as an js,hhc1nyt. )6 jo;xuecho in 20 ms after transmission. How far away is the reflecting objec. )h1,hu6xjys coj;tnt?
A. $1.5 \; km$
B. $3.0 \; km$
C. $6.0 \; km$
D. $9.0 \; km$
