Прямая ОА перпендикулярна к плоскости ОВС, и точка О является серединой отрезка AD. Докажите, что: a) AB = DB; б) AB=AC, если ОВ=ОС; в) OB = OC, если АВ=АС

Cuckoos do not build nests. They use the nests of other birds
She usually drinks coffee, but today she drinks tea
I'm busy at the moment. I am redecorating the room
-How do you get to work as a rule? - I usually go by bus, but tomorrow I will go in Tom's car
Do you always write with your left hand?
This car makes a very strange noise. Do you think it is alright?