—Jenny, do you want to be a doctor in the future?
—No, my mom expects me a doctor but I want to he a teacher.
A:be
B:is
C:was
D:to be
(Ⅰ)求证:平面AA1B1B⊥平面BB1C1C;
(Ⅱ)若D是CC1中点,∠ADB是二面角A﹣CC1﹣B的平面角,求直线AC1与平面ABC所成角的余弦值.