Cho phương trình a x 2  + bx + c = 0 (a  ≠ 0) có biệt thức  △ = b 2  - 4ac. Phương trình đã cho vô nghiệm khi:

A.  △  < 0

B.  △ = 0

C.  △ ≥ 0

D.  △ ≤ 0

Read the passage and answer the questions

I have a lot of friends. Of all my friends Nga, Ha, and Lan are the ones I spend most of my time with. Nga is the most sociable. She is a hard - working student who always gets good marks. After school she often helps her parents with the housework. Ha and Lan are kind but reserved in public. Ha has short hair and fair skin. She likes playing the piano. Lan is the tallest. She likes playing chess. We often go to the movie to see some new film at weekends.

What do they often do at weekends?