Biết nguyên tố X có NTK bằng 5/2 nguyên từ oxy. X là nguyên tố nào

Exercise 4. Read the following passage and mark the letter A, B, C or D to indicate the
correct answer to each of the questions.
Nam’s grandparents live in a nice, small house in the countryside. There isn’t a school, a
bookshop, a hotel, a hospital, a restaurant near it but there is a long river. There is a rice
paddy behind the house. There is a rice paddy in front of it, too. To the left of the house,
there is a small market. To the right of the house, there is a big garden. His grandparents
grow a lot of vegetables and flowers there. He loves them and their house very much. It is
quiet and peaceful. He visits it every summer.
1. Near Nam’s grandparents’ house, there is ___________________
A. school B. a bookshop C. a restaurant D. a long river
2. What is behind the house?
A. a big garden B. a rice paddy
C. a long river D. a small market
3. Is there a rice paddy in front of the house?
A. No, there’s. B. No, there isn’t. C. Yes, there is. D. Yes, there
is
4. What’s there to the right of the house?
A. a big garden B. a rice paddy
C. a long river D. a small market
5. Why does he visit the house every summer? – Because ___________________
A. He loves that house.
B. He doesn’t like his house.
C. His parents live in that house.
D. He loves his grandparents and that house.
jup em vs!

Một hiệu sách có 2021 quyển sách được xếp vào các giá sách. Mỗi giá sách có 5
ngăn, mỗi ngăn có 20 quyển sách. Cần ít nhất bao nhiêu giá sách để xếp hết số sách trên?

S=8+8^3+8^5+...+8^2x+1, x lớn hơn hoặc bằng 1, x thuộc N