题目

When I was a child, I often dreamed of the time when I could leave home and escape to the city. We lived on a farm and, in the winter especially, we were quite cut off from the outside world. As soon as I left school, I packed my bags and moved to the capital. However, I soon discovered that city life has its problems too. One big disadvantage is money—it costs so much to go out, not to mention basics like food and housing. Another disadvantage is pollution. I suffer from asthma(哮喘), and at times the air is so bad that I am afraid to go outside. Then there is the problem of trave下列画图语言表述正确的是（   ）   A.延长线段AB至点C，使AB=ACB.以点O为圆心作弧   C.以点O为圆心，以AC长为半径画弧D.在射线OA上截取OB=a，BC=b，则有OC=a+b