In the graphic, Host A has reached 50% completion in sending a 1 KB Ethernet frame to Host D when Host B wishes to transmit its own frame to Host C. What must Host B do?

In the graphic, Host A has reached 50% completion in sending a 1 KB Ethernet frame to Host D when Host B wishes to transmit its own frame to Host C. What must Host B do?

Host B can transmit immediately since it is connected on its own cable segment.
Host B must wait to receive a CSMA transmission from the hub, to signal its turn.
Host B must send a request signal to Host A by transmitting an interframe gap.
Host B must wait until it is certain that Host A has completed sending its frame.

ccna exploration 1 chapter 9 Exam Question And Answers 

In the graphic, Host A has reached 50% completion in sending a 1 KB Ethernet frame to Host D when Host B wishes to transmit its own frame to Host C. What must Host B do?