Apple’s i Phones _____easy to learn. Many young people can use them well. 

 The world’s population is getting larger and larger, so scientists will have to ______ new ways to solve food problem.

It will _______ hundreds of years to make robots think like a human.

—Why not take this sweater, Li Hua?—I have only 20 yuan. I can’t _____ it. 

It ____ me two hours to finish the work last night.