The hottest topic in Yongjin Middle School，it's money. The school held an activity called “making money” last weekend．About 200 Junior1and Junior 2 students were divided into 30 teams．They went out to make money by selling things．
Some sold newspapers；some chose bottled water；some sold environmentally friendly shopping bags．
      Hu Qing's team decided to sell some useful books in Activity Center．They thought parents would like to buy the books for their children．But unfortunately，they met urban management officers．The officers asked them to leave．“Finally we had to give up.” said Hu．
       Wang Bing and her team sold ice cream in a square．They didn't meet any officers．But few people were interested in what they were selling．The team then put up a board saying “For Country Kids”．It worked．More people came to their stall（小摊）．A foreigner even gave them 100 yuan. Later that day they gave the money to the “Project Hope” office．
      Meng Zhaoxiang and his team were luckier．They sold all their cakes in four hours．They made 40 yuan．“It was not easy to make the money，” said Meng．“Some people just looked．Others just tasted but didn't buy．Now I know how hard it is for our parents to make the money we need to lead happy lives．”

等轴双曲线$C$的中心在原点,焦点在x轴上,$C$与抛物线$y^2=16x$的准线交于$A,B$两点,$\left|AB\right|=4\sqrt{3}$;则$C$的实轴长为(   ）

如图，AB是⊙O的直径，点C是⊙O上的一点，若BC=6，AB=10，OD⊥BC于点D，则OD的长为____ .