王刚同学在学习了解直角三角形及其应用的知识后，尝试利用所学知识测量河对岸大树AB的高度，他在点C处测得大树顶端A的仰角为45°，再从C点出发沿斜坡走2√10米到达斜坡上D点，在点D处测得树顶端A的仰角为30°，若斜坡CF的坡比为i=1:3（点E,C,H在同一水平线上）．
（1）求王刚同学从点C到点D的过程中上升的高度；
（2）求大树AB的高度（结果保留根号）．
—Look! There are so many people in the restaurant.
—Yes. The food there ________ be delicious.
—____________ we leave the library before 5 o'clock?
—No, you needn't. You can stay here until 5:30.
The biggest challenge weall face is to prevent further environmental disasters. We ________ take action before it is too late.
Listen up, guys!Everyone ________ wear a mask. Go and buy one if you don’t have one.
—Must I return this book before Friday, Sir?
—No, you ________,dear. You can keep it for two weeks.
You’d better take an umbrella when you go out, because it ________rain.
The man _______ be a doctor in this hospital, but I’m not sure.
—Whose notebook is this?
—It ________ be Alan’s. It looks like his.
Mary ________ go to London next year but she is not sure.
