Thanks for=Thank you for
为……而感谢
Thanks to（…because of）
幸亏

let's do sth表示建议，反意疑问句用“shall we”
let us do sth表示请求他人允许，反意疑问句用“will you”
Let's go ,shall we?（指说话人邀请一起走）（包含听话人在内）
Let us go,will you?（指说话人请求你同意他/她走）（不包含听话人在内）

Sound travels slower than light

need
need for"需要……去做……","对……的需要"
in need of
可做情态动词，后加动词原形
need doing=need to be done

help sb with sth=help sb to do sth

either or不是 就是/要么 要么
either
Either you come in or you blast off.
你要么进来，要么就走开。
例题：Unfortunately I was sitting at the table with smokers on either side of me
side如果是复数就要用both，either后面加可数名词单数
neither nor不是 也不是
No matter how careful you are, you can neither nor control the future. So you mustdiversify.
不管你多么小心，你都不能预知或控制未来，所以你必须分散投资。
neither of them

It takes sb. some time to do sth

sentences
If you know the answers, please put up your hands high above your heads.

finishi doing sth.