The computer system _______suddenly while he wassearching for information on the Internet.

Landing safely in bad weather is a _______ task for any pilot, and even the smallest error can lead to a disaster.

. It is so nice to hear from her. ______, we last met more thirty years ago.

When I talked with my grandma on the phone, she sounded weak, but by the time we ______ up , her voice had been full of life

(2013·长沙二模)—The research on the new flu virus vaccine is challenging and demanding.Who do you think can do the job?—________ my students have a try?