Since David ______ downloaded a virus into his computer, he can not open the file now.

 I’d like to start my own business next year – that’s _________ I will face my big challenge in life.

“Perhaps we need to send for Dr. Smith to see what we can do about it,” Father suggested ________ to his neighbor who had come to discuss the problem.

A man may usually be known by the books he reads _____ by the friends he keeps.

 When they knew there was a panda in the zoo, the children could ___ wait to see it.