锚地、停泊场、航道和重要海区及底质复杂海区，底质点密度一般为图上（）平方厘米一个点。
A、1~4
B、4~9
C、9~16
D、16~25
参考答案：C
In order to improve English _____.
A．Jenny’s father bought her a lot of tapes
B．Jenny bought a lot of tapes for herself
C．a lot of tapes were bought by Jenny
D．a lot of tapes were bought by Jenny’s father
MRCP扫描最合理的层厚是（）
A.2～3mm
B.7～9mm
C.9～10mm
D.3～4mm
E.以上都不好
