There was a grocery shop in a town. Plenty of mice lived in that grocery shop. Food was in plenty for them. They ate everything and spoiled all the bags. They also wasted the bread, biscuits and fruits of the shop.
The grocer got really worried. So, he thought "I should buy a cat and let it stay at the grocery. Only then I can save my things."He bought a nice, big fat cat and let him stay there. The cat had a nice time hunting the mice and killing them. The mice could not move freely now. They were afraid that anytime the cat would eat them up.
The mice wanted to do something. They held a meeting and all of them tweeted "We must get rid of the cat. Can someone give a suggestion"?
All the mice sat and brooded. A smart looking mouse stood up and said, "The cat moves softly. That is the problem. If we can tie a bell around her neck, then things will be fine. We can know the movements of the cat".
“Yes, that is answer," stated all the mice. An white mouse slowly stood up and asked, "Who would tie the bell?" After some moments there was no one there to answer this question.

 What is an intelligent mouse? Why?

Theo thuyết $\text{Orbital}$Orbital phân tử có thể dự đoán bậc liên kết và từ tính của $B_2$B2 là?

$A.$A. $1,$1, thuận từ

$B.$B. $2,$2, nghịch từ

$C.$C. $1,$1, nghịch từ

$D.$D. $3,$3, thuận từ

Trong một kho chứa cam có 42% cam Trung Quốc, 24% cam Thái Lan, 26% cam Campuchia và 8% cam Việt Nam. Trong đó, tỷ lệ cam hỏng của Trung Quốc, Thái Lan, Campuchia và Việt Nam lần lượt là 20%, 10% ,12% và 2%. a) Tính tỷ lệ cam hỏng trong kho? b) Biết một người đã mua phải một trái cam hỏng. Tính xác suất để trái cam ấy không của Việt Nam?