Polar bears liveon sea ice，which they use as a platform for hunting seals

To their disappointment, they found the lecture given by the professor difficult__________.

Would you like to go to the cinema with metonight— I’d like to, but it remains ________whether I can finish my homework in time.

Generous public funding of basic science would ________ a good many benefits for the country’shealth,wealth and security.[ ]

I want to have a rest. I feel _____ tired.