What?? What is the question? To appear six computer??
Your answer should be WHO.
Think of it like this: You wouldn't say "The boy it (a variant of 'which')", because it simply just sounds odd. Instead, you're wired to think "The boy, he (an unknown name, so it would be 'who')".
I believe the correct answer is the second choice: <span>We walked through the Red Oak Nature Center today; it was surprising how many bicyclists were there.
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