题目

To help ordinary people _________ to cholera(霍乱),John Snow wanted to use his knowledge to solve this problem.    A. exposed       B. opened         C. linked          D. joined 答案：A如图，在△ABD和△ACE中，AB=AD，AC=AE，∠BAD=∠CAE，连接BC、DE相交于点F，BC与AD相交于点G．求证：BC=DE．