c,                        x⁴+2x³-2x²+2x-3 = 0
<=> (x⁴-x³)+(3x³-3x²)+(x²-x)+(3x-3) = 0
<=> x³(x-1)+3x²(x-1)+x(x-1)+3(x-1)  = 0
<=>                   (x-1)(x³+3x²+x+3) = 0
<=>                 (x-1)[x²(x+3)+(x+3)] = 0
<=>                       (x-1)(x+3)(x²+1) = 0
<=>                                        x-1  =0  hoặc x+3=0   ( vì x²+1 khác 0 )
<=>                                            x =1 hoặc      x= -3

Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following sentences.

The government is aiming at50% reduction in unemployment.

A. at /of

B. in/ to

C. on/ at

D. at /in