图中的五角星是用螺栓将两端打有孔的5根木条连接而构成的,它的形状不稳定.如果用在图中木条交叉点打孔加装螺栓的办法来达到使其形状稳定的目的,且所加螺栓尽可能少,那么需要添加螺栓( )
Terry and his team members were the first how the disease spreads from animals to humans.
如图,AB是半圆的直径,点D是弧AC的中点,∠ABC=50°,则∠DAB等于( )