题目

______, important advances have been made in medicine and environment science thanks to increasing computer power. A . By accident B . After all C . In addition D . On average 答案：C 如图，直线，点A1坐标为(1，0)，过点A1作x轴的垂线交直线于点B1，以原点O为圆心，OB1长为半径画弧交x轴于点A2；再过点A2作x轴的垂线交直线于点B2，以原点O为圆心，OB2长为半径画弧交x轴于点A3，…，按此做法进行下去，点An的横坐标为 [　　] A． B． C． D．