a) Cho x,y,z là các số dương thỏa mãn x²+y²+z²=3, tìm giá trị nhỏ nhất của F=\(\dfrac{x^2+1}{z+2}\)+\(\dfrac{y^2+1}{x+2}\)+\(\dfrac{z^2+1}{y+2}\)

b) Với a,b,c > 0 thỏa mãn ab+bc+ca=3, chứng minh rằng
\(\sqrt{\dfrac{a}{a+3}}\) +\(\sqrt{\dfrac{b}{b+3}}\)+\(\sqrt{\dfrac{c}{c+3}}\)\(\le\)\(\dfrac{3}{2}\)

Visual pollution has a greater effect on people than you may think.
I remember when I went to a foreign city, I was really scared because there was so much graffiti on the buildings' walls. Then I looked up, and I saw a lot of power lines over my head. Although they were not dangerous, I still felt insecure since I thought they might fall down. These things prevented me from enjoying the beautiful sights of the city.

I also remember the time I studied in Melbourne. Once I was so busy with my assignments that I did not tidy my room for two weeks. Looking at the messy room caused me so much stress that I did not want to study. Then I decided to clean the room and put my things in their proper places. I also bought a small plant and placed it in a corner. These simple actions increased my motivation and helped me to focus on my lesson.

1. What did she feel after the room was tidied?
A. She could concentrate on her studying.
B. She was motivated to buy a small plant.
C. She was motivated to tidy the room again.
D. She felt motivated to concentrate on tidying the room