Some physics problems in this book are _________difficult for the students _________work out.

—I hope to make decisions by myself. —OK. But remember _____________ you do, you should think about the results.   

I enjoyed your lecture very much, ______ there were some parts I couldn’t quite understand. 

 --___________ is your phone number? --It’s 86502566. 

The beginning of the movie was boring, ______ the end was amazing!