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

They have so many (A) children that they can’t (B) afford sending (C) them all (D) to university

A. so many

B. can’t

C. sending 

D. all

a) \(x^2=7\Rightarrow x=+-\sqrt{7}\Rightarrow\) x k là số hữu tỉ

\(x^2-3x-1=0\Leftrightarrow\left(x^2-3x+\frac{9}{4}\right)-\frac{13}{4}\Leftrightarrow\left(x-\frac{3}{2}\right)^2=\frac{13}{4}\Leftrightarrow x=\frac{3+-\sqrt{13}}{2}\)=> x k là số hữu tỉ

\(x=\frac{1}{x}\Leftrightarrow x^2=1\Leftrightarrow x=+-1\). mà x khác 2 gtrị này => k có x t/m