The answer is A., it makes it feel as if you're shouting at the reading. Exclamation marks are used to show lots of emotion, as sometimes it is also used for shouting.
B., C., and D. all are completely not related.
Your opinion can be expressed with exclamation marks, it won't confuse anyone. Like I said, exclamation marks are used to show lots of fire and emotion. It wouldn't confuse anyone.
Exclamation marks do not confuse the main point. The reasoning for why it isn't C is similar to the reasoning for B. Exclamation marks do not change the main point.
C. is pretty much the opposite. Exclamation marks are used for emotions, not to show no emotion.
Answer:
<em>D. To explain the origin of Dorothy's slippers and the Wicket Witch</em>
