Only that factory ______ yesterday ______this kind of machine.
There are 40 students in our class,who come from a ________of backgrounds.
—Hi,Peter. Long time no see. —Oh,it’s you,Jack. I’m sorry I didn’t ________ you at first.
People are encouraged to speak openly,but careless words are ________to hurt others’ feelings.
Our bodies are strengthened by taking exercise. ________,our minds are developed by learning.
Smoking is one of the ________causes of cancer,killing millions of people each year.