已知四棱锥S-ABCD,底面为正方形,SA⊥底面ABCD,AB=AS=a,M、N分别为AB、SC中点.(Ⅰ)求四棱锥S-ABCD的表面积;(Ⅱ)求证:MN ∥ 平面SAD.
The number of divorces in the first six months of this year nearly halved after China introduced a 30-day cooling-off period before divorce in last year's newly adopted Civil Code. Since the new rule came into effect on...
English is considered as a(n) language,and it is no surprise that there are so many people in the world learning English. [ ]A.universal B.logicalC.artificial D.regular