bit 侧重指微小，一点点，小碎片。
piece 最普通用词，多指从整体上分割下来的东西，可大可小。
sheet 侧重指平整很薄的一张或一片。
slice 多指切得很薄的一片食物。
fragment 指破裂的，不完整的，不可完整的碎片。
scrap 侧重指废弃的零碎之物。
参考例句
1. The detectives tried to piece together the facts. 侦探们说法把所有的事实拼凑在一起。
2. He gave us a piece of useful information. 他给我们提供了一条有用的信息。
3. To feed on the herbage of (a piece of land). 放（牲畜）吃（一块地上的）草。
英英解释
n.
1. a separate part of a whole
2. an item that is an instance of some type
3. a portion of a natural object
4. a musical work that has been created
5. an instance of some kind
6. an artistic or literary composition
7. a portable gun
8. a serving that has been cut from a larger portion
9. a distance
10. a work of art of some artistic value
11. a period of indeterminate length (usually short) marked by some action or condition
12. a share of something
13. game equipment consisting of an object used in playing certain board games v.
1. to join or unite the pieces of
2. create by putting components or members together
3. join during spinning
4. eat intermittently; take small bites of
5. repair by adding pieces
