A housing bubble is an economic situation _____ occurs when house prices rise much too

 A housing bubble is an economic situation _____ occurs when house prices rise much too fast.

A. which            B. where                 C. what               D. why

One possible student version:

Campus Security

     Security issue has always been one of our main concerns, and when it comes to the campus security, we have to take it more seriously. Nearly every day, there are reports to the security office on campus that valuable things are stolen. A surrounding with stealing can’t be worse for studying. In such cases, what measures should be taken to improve the campus security?

    On the one hand, we students should strengthen our security awareness. Once we find something unusual, we should report it to the campus guard immediately. On the other hand, more equipment such as monitors should be installed on campus so as to detect crimes as soon as possible. Besides, a proper number of security guards should be arranged to walk around the campus.

    In my opinion, campus security will be improved as long as we work together and schools will try their best to make everyone on campus safe and sound.