Căn bậc hai số học của -81 là ?

The scientists haveachieveda breakthrough in cancer research.

She set out her stall firmly and precisely, and had very clear ideas what she wanted to do.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 40 to 46.

Read the following passage and mark the letter A, B, C, word or D on your answer sheet to indicate Correct or phrase that best fits each of the numbered blanks from 35 to 39.

All students in our school are always required to wear his uniforms when they go to school.

The collectable knowledge of the indigenous population proved invaluable in guiding the conservation efforts for the endangered rainforest.

Cindy forgets to bring her notebook to the biology class yesterday morning.