@duongthang - Please underline the part of the sentence that needs to be corrected. Also, for the benefit of others, please mention the complete question with all the answer choices. Thanks!

Question:
In a leveraged buyout, investors borrow huge sums of money to buy companies, hoping to pay off the debt by using the company's earnings and to profit richly by the later resale of the companies or their divisions

a, by using the company's earnings and to profit
b,
c,
d,
e, with the companies' earnings and to profit

(A) says - by using the company's earnings - referring to just ONE company. Where as the statement says
investors borrow huge sums of money to buy companies

They borrow money to buy MULTIPLE companies, more than one. Thus, they will use the money from all these companies, or "with the companies' earnings...." as (E) puts it.

Hope it helps.