a, Ta có: C(x) - B(x) = A(x)

=> C(x)=A(x)+B(x) 

       A(x) = x6 - 2x5 + 9x4 + 5x3 - 4x + 7

       B(x) = -x6 - 2x5 + 9x4 - 5x3 + 2x – 7

A(x)+B(x)=       -4x5+18x4            -2x

Vậy C(x)= -4x5+18x4 -2x

-Những loài động vật ở môi trường đới lạnh có những đặc điểm thích nghi  đối với môi trường sống:

+ Bộ lông dày giữ nhiệt cho cơ thể

+ Mỡ dưới da dày giữ nhiệt dự trữ năng lượng chống rét

+ Lông màu trắng mùa đông dễ lẩn với tuyết che mắt kẻ thù

+ Ngủ trong mùa đông, di cư về mùa đông

+ Hoạt động về ban ngày tỏng mùa hạ

A-chuột nhảy

1. The last time I have played tennis since 1990

2. The tourist asked me if Phong Nha was the most beautiful cave in Viet Nam

3. The room has been cleaned before I got home

4. They held an English- speaking contest for students

1. She has long black hair

2. Her eyes are small

3. Her face is round

4. The library had many people yesterday

1.organises

1.D

2.B

C-shall we

1. D-how often

2. A-although

1. were watching/came

2. to play

3. has been

4. was watching

5. going

6. haven't eaten

7. telling

8.write

9. wrote

10. were you doing

11. lived

12. has lived/was

1. Sources of energy will be used more effectively for our future.

2. I have never gone to London before

3. You like English, don't you?

4. Although It was noisy, the students continued studying.

5. The weather used to be bad in November 

M(x)+N(x)=(3x⁴+2x³-x²+2)+(x⁴-2x³+2x-1)

= 3x⁴+2x³-x²+2 +x⁴-2x³+2x-1

=(3x⁴+x⁴)+(2x³-2x³)-x²+2x+(2-1)

=2x⁴+2x³-x²+2x+1