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

.Mary quickly closed the door of her room _______ her father could reach it to keep him out.

---I think the company may not offer you a good pay.---_______, I won’t take the job.

—I heard Charlotte had been drowned in the lake.—Really！Her boat turned______,and ______she couldn’t swim.

However weak we are，we can still do something against the powerful nature so long as we are     prepared．