如图， AB与⊙O相切于点B，线段OA与弦BC垂直于点D，∠AOB=60°，BC=4cm，则切线AB= cm．
There are /ten/students in our group．
I /həup/you will succeed．
In spring，Kunming is /′wɔ：mə/than Liaocheng．
There's （厚的）ice on the lake．
Alexander Bell （发明）the telephone in 1876．
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