Mr. Rock teaches maths at a secondary school. He knows well of his neighbours except the man who lives next door. The man never speaks to anyone and no one knows what he does to make a living .

One day, when Mr. Rock came home from work , he found a gold necklace outside his door. Mr. Rock wondered where it came from. He thought that perhaps someone had dropped it. Mr. Rock planned to take it to the police station the next day. He thought the police would be able to find the owner.

Just then, the police came to Mr. Rock’s home and saw the necklace in his hand. Mr. Rock was very shocked when he was accused(起诉) of robbery(抢劫). A policeman told him that a jewellery shop had been robbed. A witness said that she had seen someone run from the jewellery shop into Mr. Rock’s building right after the robbery.

Mr. Rock was not the robber, but how could he prove it?

小题1:What’s Mr. Rock’s job? （不超过5个单词）____________________________________

小题2:Where did he find the necklace? (不超过3个单词) _______________________

小题3:Why did Mr. Rock feel shocked? (不超过6个单词) ________________________

沿光滑的竖直墙壁用网兜把一个足球挂在A点(如图)，足球受到的重力为G，网兜的质量不计。悬绳与墙壁的夹角为α=30^o。悬绳给球的拉力为，墙壁给球的支持力为，下列表述正确的是（ ）

A．大于G

B．小于G

C．与的合力一定竖直向上

D．与大小之和等于G