calling crab的用法和樣例：
例句
- Even without daylight the crab's skin colour continued to change exactly on time.
即使沒有陽光，招潮蟹的皮膚仍可以變換顏色。 - But when an enterprising scientist placed a fiddler crab in darkness,he was amazed to find that the color of the crab's shell kept ticking off the time with the same accuracy.
但是，當一個勇於探索的科學家把招潮蟹放在黑暗中，他驚訝的發現蟹殼的顏色依然準確的按時間轉變。
