When forbidden to surf the Internet, teenagers often _____ surfing it, saying that it provides them with colorful entertainments, a convenient means of communication as well as useful information

It is a surprise for me to see that theseold-fashioned machines are still ________ in the big city.

By the time you finish the book, you _______________ more about Chinese history

My teacher helps us _______ swimming.

The government should _________ the use of new types of energy to make a greener world.