Some young people in America are expected to leave ______ could be life’s most important decision—marriage— entirely up to luck.

Now China is fighting against illegal cooking oil（地沟油）, a kind of waste oil _____can cause a lot of illness.

It’s very difficult ______ you to get the tickets ______ the World Cup. [ ]

The streets here are not so ____ as those in our city.

They argued _________ each other ________ the math problem yesterday.