But personally I believe a business letter should end with Very truly yours, not Sincerely.
还行,乔治。但是我个人相信一封商业信函应该以“敬上”结尾,而不是“谨启”。
But I'm worried about his Chinese.He may fall behind the other students when he comes back.
但我担心他的中文。等他回来后,他可能会落到其他同学后面。