(2014·苏锡常镇四市调研)—As a teenager，our son should have two or three hobbies to be really happy.—________，but how can he afford the time with so much homework every day?

Thank you for the trouble you have ____ to help me. 

In my opinion, Jack, though relatively stubborn, was not too difficult ___.

The snow is so deep. We can hardly get out of the house, ______?

Further space exploration has been _______ with the rapid development of China’s science and technology.