giúp mình với đoạn văn hơi dài cảm ơn a

Exercise 3: Read the passage and answer questions below.
A. A UFO (Unidentified Flying Object) is any object flying in the sky which cannot be identified by the person who sees it. Sometimes this kind of object is investigated. If people can still not figure out what the object is after investigating, it is called a UFO. If they figure out what the object is, it can no longer be called a UFO because it has been identified.
B. UFOs can be anything, but people often use the word "UFO" when they are talking about aliens. Aliens are beings from other planets not Earth. When talking about aliens and UFO, people tend to think about Mars or Venus. Many people believe that aliens are so intelligent that they can create UFOs to come to other planets, while some think they visit different planets to invade and settle down.
C. Studies estimate that 50%-90% of all reported UFO sightings are identified later. Usually 10%-20% are never identified. Studies also show that very few UFO sightings are hoaxes (people trying to trick other people). Most UFOs are actually natural or man-made objects that look strange. 80%-90% UFOs are identified as one of three different things: astronomical causes (for example: planets, stars, or meteors); aircraft; balloons 10%-20% of UFOs are other causes (such as birds, clouds, mirages, searchlights, etc.)
Question 1-3. Choose the best headings for each paragraph of this passage.
1. Some conclusions about UFO’ reports
2. What people think about aliens
3. UFO in common thoughts

Question 4-7. Choose the correct answer A, B, C, or D.
4. What does the word “figure out” in the first paragraph mean?
A. observe B. explain C. calculate D. require
5. Another word used to describe a UFO is _________.
A. spacecraft B. astronaut C. flying saucer D. cooking oil
6. Most UFOs are identified as one of the following things EXCEPT _________.
A. stars B. balloons C. clouds D. rains
7. Which of the following sentences is NOT true?
A. UFO means Unidentified Flying Object.
B. UFO is often used to talk about alien spaceships.
C. Many UFO sightings are hoaxes.
D. Over half of all reported UFO sightings are identified.

cho tam giác ABC. điểm O nằm trong tam giác. Lấy điểm D trên OA, từ D kẻ DE//AB (E thuộc OB ) và DF // AC (F thuộc OC) .                                                                                                             a)cm OE/OB = OD/OA                                                                                                                           b) cm OF/OC = OD/OA                                                                                                                           c) cm EF//OC

Cho tam giác ABC vuông tại B có C = 50 độ 

a. tính số đo a 

b. trên cạnh AC lấy điểm D sao cho AD=AB .Tia phân giác của A cat cạnh BC ỏ E . Chung minh tam giác ABE = tam giác ADE 

c. Qua A vẽ duong thang D vuông góc voi AB . Tu B vẽ duong thang song song voi EA cat duong thang d tại F . Chung minh tam giác ABE = tam giác BAF 

d. gọi I là trung điểm của AB . chung minh ba điểm E,I,F thang hang

Cho biểu thức B= $\frac{1}{2^3}+\frac{1}{3^3}+\frac{1}{4^3}+...+\frac{1}{{2021}^3}$. Chứng minh B<$\frac{1}{2^2}$