This paper states some factors that affect the listening comprehension of college students. It focuses on loss of sound and the difference between British English and American English pronunciation.
2
最初的英音更像是今天的美音。研究表明,英式发音开始发生变化是从北美变成殖民地开始的。
The original British accent was more like the modern-day American accent, and research has shown that it is the British accent which has evolved more since colonizing of North America.
3
中国话里有很多方言,英语除了有美音和英音,是否也存在不同的方言?
That's incorrect. Within the United States there's tons of different dialects. Look up "Minnesotan accent" and "Brooklyn accent.