They _____ have arrived at lunch time but the flight was delayed.

My cousin keeps the photo ____ he can see it every day, as it always reminds him of his college days in Florida.

Did Betty go shopping with you yesterday? — Even if she _____ a lot of studying, she would have preferred staying home to going shopping. [ ]

It is generally believed that communication skills are becoming ______ it takes to be a good doctor.

I’m really busy today because I have homework to do.