---Who called just now? ---I don’t know because I didn’t______ his voice.

 The level of the river ___ 20 centimeters over the security line and ____must be taken to control the flood. 

.---You have just 15 minutes to get to the airport. ---All right. I guess I can ______.

Many difficulties have ______ as a result of the overuse of coal

When you meet a new word in reading the English papers, you can guess its meaning but needn’t always ______ the dictionary.