1. 本题是转换信息题，是根据第三段的“Our earth itself is a big magnet. So a little magnetic needle that swings freely lines itself with the big earth magnet to point north and south”而推断得来的，将定语从句that swings转换成现在分词swinging作前置定语。
2. 本题是综合信息题，根据第三段的“When people discovered that idea about a thousand years ago and invented the compass”而推断得来的，结合题干综合出该题的答案为Based。
3. 本题是转换信息题，是根据第五段的“Many birds migrate twice a year between their summer homes and winter homes”而推断得来的。根据题干将migrate转换成相应的名词migration。
