Polar explorers have to be extremely______ to bear the climate and other hardships. [ ]

______, I lost heart in English learning, but myteacher often said to me, “Keep on working hard; you’ll succeed _______.”

The sign means _____.

(2013·吉林四校高三一诊)I really don’t know how to thank you, but for your help, I ________ my lost necklace.

I feel it hard to keep up with my classmates. But whenever I want to ， my teacher always encourages me to work harder.