He is careless a student that he often some letters while writing.A. such; leaves onB. s

问题补充：

He is careless a student that he often some letters while writing.

A. such; leaves on

B. so; leaves off

C. so; leaves out

D. such; leaves out

答案：

A. such; leaves on

B. so; leaves off

(答案→)C. so; leaves out

D. such; leaves out

解析：考查so,such用法和固定词组。So+adj+a/an+单数名词=such a/an adj+单数名词。本题中的so careless a student=such s careless student.如此粗心的学生。Leave out遗漏；leave off停止做某事，戒除…句意：他是一个如此粗心的学生以至于他在写作的时候介词遗漏一些字母。故C正确。