What does the author mean by saying“but it's one thing to improve a person's ability to see words and quite another thing to improve his ability to read a test efficiently.”in the second paragraph? (  )

• A、 The ability to see words is not needed when an efficient reading is conducted.

• B、The reading exercises mentioned can't help to improve both the ability to see and to comprehend words.

• C、The reading exercises mentioned can't help to improve an efficient reading.

• D、The reading exercises mentioned have done a great job to improve one's ability to see words.