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

— How do you find his new novel?    — His previous ones are great, and I think this one is _____ worth reading.

There was such a long queue for coffee at the intervals that we __________ have to give up.

Nancy reminded me of what I should ________ have forgotten.

The technology of electronic products is ________changing, so you needn’t follow the fashion.