Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.

Question 11: Blues is a form of music that came from the American South, where slaves on plantations _______ spiritual songs and word music.

A. will sing

B. would sing

C. must sing

D. should

Cho hàm số f ( x ) = a x 4 + b x 2 ( a , b ∈ ℝ )  có đồ thị hàm số f'(x) như hình vẽ bên dưới. Biết rằng diện tích phần tô đậm bằng  1 8 . Phương trình 8f(x) + 1 = 0 có bao nhiêu nghiệm?

A. 0

B. 4

C. 3

D. 2

Mark the letter A, B, C or D to indicate the underlined part that needs correction in each of the following questions.

Question 6: Modern art is on display at the Guggenheim Museum, a building with an unusually design.

A. Modern art

B. display

C. a building

D. unusually