连接抛物线上任意四点组成的四边形可能是（ ）（填写所有正确选项的序号）．
①菱形
②有3条边相等的四边形
③梯形
④平行四边形⑤有一组对角相等的四边形
②③⑤
Having studied the INMARSAT document, GMDSS document, SOLAS Convention and other international navigation documents, we all know that the Chapter IV of SOLAS Convention is mainly about（）.
A.the radio regulations
B.the technical terms and definitions
C.how to operate the GMDSS SES equipment
D.Maritime Communications
一般锚桩的埋设分为（）种。
A、1
B、2
C、3
D、4
