Signing the contract and sending it back to you is no problem .The problem is we are waiting about 10 Containers which a

Signing the contract and sending it back to you is no problem .The problem is we are waiting about 10 Containers which are on the way right now and need to pay for them .Which of the course means we will not be able to pay your deposit in the near 10 days .关于此句中：which of course的用法,是怎样的语法现象呢?