—Would you mind _______ the answer on the blackboard, sir? We can't follow you.
—OK, I'll do it now.
A:write
B:writing
C:to write
D:wrote
如图,⊙O的直径AB=6,CD是⊙O的弦,CD⊥AB,垂足为P,且AP∶BP=2∶1,则CD长为____ .
电话通信与网络通信(电子邮件)有许多相似之处,如图所示,两图表示出两种通信的工作原理,比较两者可以发现: