看美劇學英語：The coast is clear(安全，沒危險)
As soon as the coast was clear he climbed in through the window. 等到四下無人，他便從窗戶爬了進去。
看劇學英語：It's not rocket science(並非難事；不是很複雜)
Okay.I got you.If you say The coast is clear, you mean it is safe to do something or go somewhere because no one is watching or listening who would prevent you or catch you:
用英語It's safe to do something理解和記憶英語the coast is clear足矣！也是重點，不是它的中文。至於剩下的英語，感覺難就不記，容易就記一下。
You can come out now, the coast is clear.
附：查英英字典 Yahoo coast is clear meaning
1.Cambridge: it is safe to do something or go somewhere because no one is watching or listening who would prevent you or catch you:
You can come out now, the coast is clear.
2.Collins: If you say that the coast is clear, you mean that there is nobody around to see you or catch you.
用詞有別，意思不變，為什麼不直接用它們記憶coast is clear？又能豐富我們的英語表達用詞。
You can come out now,' he called. 'The coast is clear. She's gone
我們的英語學習，「學」是一回事，「用」英語又是一回事。我不知道在你漫長的英語過程中，你就算「學了」這句英語coast is clear，你在日常生活工作中有機會跟人「用」它的機率有多大呢？估計一輩子都沒有機會「用一次」。既然如此，你只用中文「學會」這句基本「沒用」的英語意義何在？
還是「用」英語學吧，管它以後有沒有「用」，至少現在能把(已知的)英語用起來學它。