Chinese - Help Requested!

Can anyone help me with the following sentences? I would like to know if the Chinese is correct or not.

Any help would be really appreciated.

I'm a native English speaker, I could correct something of yours if you wish ~

Thank you for your help. 

你的 中文发音 很 好。Your Chinese pronunciation is very good.
他的 中文发音 很 好。His Chinese pronunciation is very good.
同学的 中文发音 很 好。My classmate's pronunciation of Chinese is very good.
我的 朋友的 中文发音 很 好。My friend's Chinese pronunciation is very good.
我的 中文发音 不 好。My Chinese pronunciation isn't good.
他的 中文发音 好 吗? Is his Chinese pronunciation good?
他的 中文发音 不 好。His Chinese pronunciation isn't good.
这位 老师 发音 很 好。The teacher's pronunciation is good.
这位 老师 发音 不 好。The teacher's pronunciation is not good.
这个 字 怎么 发音? How do you pronounce this word?
请问, 这个 字 怎么 发音? Excuse me, how do you pronounce this word?
我的 学生们 发音 不 好。My students' pronunciation is not good.
我的 学生们 英语发音 不 好。My student's English pronunciation is not good.
刘 先生 英语发音 不 好。Mr. Liu's English pronunciation is not good.
王 小姐的 发音 太好了。Ms. Wang's pronunciation is extremely good.
郑 先生的 发音 太好了。Mr. Zheng's pronunciation is extremely good.
朱 小姐 的 发音 太好了。Ms. Zhu's pronunciation is extremely good.
他的 发音 太好了。His pronunciation is extremely good.
 这位 老师 发音 清。The teacher's pronunciation is clear.
他 发音 清。His pronunciation is clear.
他 发音 不 清。His pronunciation is not clear.
 

These sentences are all correct.

hehe… help each other, boys & girls!

How long time do I need to studying chinese for making conversations..

“His pronunciation is clear” u’d better translate like this “他的发音很清楚/清晰” not “他发音清”

All look great.