“If I ________ taking drugs, I would be a successful businessman now,” said the dying drug addict. 

 Look out! Don’t get close to the building. It _________.

—I guess you can buy such a smart phone for 300 dollars. —I could just two months ago，but the price ________ by 20%.

A red light will start continuously flashing when the batteries____ low.

They ________ to enter the building by the back door; however, the front door was locked.