Все грани параллелепипеда ABCDA1B1C1D1 — квадраты. Найдите величину двугранного угла, который образован сечениями AB1C1D и CB1A

1)Now you can speak French?
3)Tom could not make it last week
6)he can only get there in the evening
7)Can I take your pencil?
8)She had to go and tell the whole story
15)Peter should not be missed so many lessons
26)We do not need to wait any longer