Giải phương trình:  5 x 2 x   +   2   +   1   =   - 6 x   +   1

Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
Question 9: ________ research team is an effective way to prepare for class preparation of social studies such as history, geography, literature and economics.

A. Form

B. Forms

C. Forming

D. Formed