开具发票应按照规定的时限．顺序，逐栏．全部联次一次性如实开具，并加盖单位财务印章或发票专用章，特殊情况也可以分联次开具。( )

What is the MOST important thing you should do before transmitting on a marine radio? （）

A.Ask for permission

B.Record the time in your radio log

C.Press the push to talk button three times

D.Monitor the channel to insure that it is clear