P、Q是一列简谐横波中的质点，相距30m，各自的振动图象如图所示.

(1)此列波的频率f＝________Hz.

(2)如果P比Q离波源近，且P与Q间距离小于1个波长，那么波长λ＝________m，波速v＝________m/s.

___of them has a dictionary and ___one of them can look up words in the dictionary

A．Each,every

B．Every ,each

C．Each,each

D．Every,every