题干
Sound travels ______ air ______ a speed of about 340 metres per second.
A：over; in
B：through; at
C：by; at
D：through; over
答案(点此获取答案解析）
B
Sound travels ______ air ______ a speed of about 340 metres per second.
A：over; in
B：through; at
C：by; at
D：through; over
