Regarding some words and phrases.
There are some words and phrases in the course that I am a bit confused about. For instance, the character 谁 is pronounced "shei2". It was my understanding that this is an informal way of pronouncing the character and that a more formal way of reading it is "shui2" . Secondly, I had learned that the Chinese words for "here", "there", and "where" were 这里, 那里, and 哪里, which are erhua'd to 这儿, 那儿, and 哪儿. Are the erhua forms more common? Lastly, the word 牛 is pronounced /nju/. It was my understanding that is was pronounced /ni̯oʊ̯/. Could anyone shed light on these topics? Thank you in advance.