How can I know when the word is written with A or with O? How to distinguish them?
Hi Veronika! In Russian, all the unstressed Os are read as As. If an O is stressed it is read as an O. A stressed A is also read as an A. You have to check all words that contain Os in the dictionary to be able to spell and pronounce them correctly.
For example, the noun "корова" (cow) is read as karova because the first o is not stressed.