Hi tarek99,
Thank you for your question.
While you are
technically correct about it being a run-on sentence, this is one of the few times when breaking the rule is actually best. Let's look at the part you're struggling with in answer B, and why it's okay to break the rule in this instance:
yet the temperatures are so cold and the ice is so reflective that little of the polar ice melts during the summer
The phrases "the temperatures are so cold" and "the ice is so reflective" BOTH apply to the rest of the phrase "that little of the polar ice melts during the summer. What the writer did here is condense two sentences into one:
Sentence 1: The temperatures are so cold that little of the polar ice melts during the summer.
Sentence 2: The ice is so reflective that little of the polar ice melts during the summer.
Combined: The temperatures are so cold and the ice is so reflective that little of the polar ice melts during the summer.
By combining both sentences, it saves us from reading the same phrase twice and makes the sentence easier to digest.
Remember that English is a 90/10 language: 90% of the time, the rule is the rule - but 10% of the time it's not.
I hope this helps clear things up!
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