Nguyên tố R tạo thành hợp chất khí với hiđro có công thức hoá học chung là  RH 4 . Trong hợp chất có hoá trị cao nhất với oxi thì O chiếm 72,73% khối lượng. Viết công thức hoá học các hợp chất của nguyên tố R với oxi và hiđro.

Choose the letter A, B, C or D to complete the sentences with given words

Mekong River/ long/ river/ country.

A. The Mekong River is the longest river in the country.

B. Mekong River is the longest river in the country.

C. The Mekong River is the most longest river in the country.

D. The Mekong River is the longest river of the country

Choose the letter A, B, C or D to answer these following questions

His name is Phong. He’s twenty four years old and he’s a teacher at Nguyen Du School. This is his student. Her name is Nga. She is fourteen years old. This is his living room. In his living room, there is a table, a chair, a television and two couches.

How many couches does the living room have?

A. three couches

B. two couches

C. three couches

D. four couches