1.(上海卷,13)给定空间中的直线l及平面α,条件“直线l与平面α内无数条直线都垂直”是“直线l与平面α垂直”的()条件.(A)充要(B)充分非必要(C)必要非充分(D)既非充分又非必要2.(天津卷,5)设a,b是两条直线,α,β是两个平面,则a⊥b的一个充分条件是()(A)a⊥α,b//β,α⊥β.(B) 1. (Shanghai Vol. 13) Given the straight line l and the plane a in a given space, the condition “a straight line l is perpendicular to an infinite number of straight lines within the plane a” is the condition of “a straight line l perpendicular to the plane a.” (A) Sufficient and sufficient (B) Sufficient and unnecessary (C) Necessary and inadequate (D) Neither sufficient nor necessary 2. (Tianjin Volume 5) Let a and b be two straight lines, and a and β be two planes, then a A sufficient condition for ⊥b is (A) a⊥α, b // β, α⊥β. (B)