1 . When they came out of the mall, they discovered that their new car _________ (steal). (所给词的适当形式填空)

2 . It is said that the old coins________ under the earth for about 100 years by the time they were discovered. (bury) (所给词的适当形式填空)

3 . By the 11th century, compasses _________ (use) by Chinese to navigate their ships at sea. (所给词的适当形式填空)

4 . His several works ________ (publish) by the time he retired from the teaching post. (所给词的适当形式填空)