Answer:
D. If I want to be a doctor, I have to do well in science class.
Explanation:
In the sentence given in the question, the main purpose or point of the sentence is -
in order to become a doctor, one needs to do well in the science class.
Now, according to the cause and effect relationship of the sentence, the cause is the "<u>doing well in science class</u>" part while the effect will be "<u>becoming a doctor</u>". For the latter to happen, the former has to be done first.
Thus, to rewrite the whole sentence in a correct way, it has to be written as
"<em>If I want to be a doctor, I have to do well in science class</em>", which correctly implies the cause and effect sequence of the proposed purpose of the sentence.
