一、选择题(本大题共12小题,每小题5分,共60分,在每小题给出的四个选项中,只有一项是符合题目要求的) 1．在下列命题中,属于真命题的是( ) (A)直线m、n都平行于平面α,则m∥n．(B)设α-l-β是直二面角,若直线m⊥l,则m⊥β(C)若直线m、n在平面内α的射影依次是一个点 First, the multiple-choice questions (the title of a total of 12 small questions, each question 5 points, a total of 60 points, in each question given four options, only one is in line with the requirements of the title). Among the following propositions, the ones that belong to the true proposition are () (A) The straight lines m, n are all parallel to the plane α, then m∥n. (B) Let α-l-β be a straight dihedral angle. If the line m⊥l, then m⊥β(C) if the projections of the lines m and n in the plane α are one point in turn