Complete the questions. write the full forms: 1. - someone told alex. - really? who ? 2. - she’s trying to say something. - really? what ? 3. - somebody bought this painting. - really? who ?

1 Who told Alex?
2 What she is trying to say?
3 Who bought this painting?

Newton's great work is called "Principia" was published in 1687. More than a century ago the Russian chemical society was organazied and named after Mendeleev. The subjects in the first and second years of the students studies are very important for their future specialities. The government wasn't interested in the invention which popov made ( was made by Popov).

1) We were told about the film which was made several years before. A very interesting article which is published in the magazine is available in our library. The instrument is made of the new material. We don't know much about this subject. We heard so much about the cosmonauts who came to our town. Have you seen the new device's main components it consists of? 

ОБА варианта верны.
1) Mother`s bag- здесь использован притяжательный падеж. Существительное Mother`s стоит в притяжательном падеже, отвечает на вопрос чей?чья?=сумка чья?=мамы=мамина сумка
Необходимо помнить, что существует ещё конструкция с предлогом of, которую можно использовать ВМЕСТО притяжательного падежа. Она полностью заменяет существительное в притяжательном падеже. Данный предлог соответствует родительному падежу в русском языке и отвечает на вопрос кого? чего?
2) Bag of mother=сумка кого?=мамы=мамина сумка

Дополнение к ответу: с предлогом of употребляются ЛЮБЫЕ существительные(и одуш. и неодуш)