Read the excerpt from Team Moon. So they came by the thousands—kids, really, twenty-somethings, a few in their thirties. No one knew for sure how to get to the moon, how to land, or get home. But their goal was clear-cut, and that was enough. That gave them purpose: a reason to puzzle out the problems and seek solutions rather than sleep.

Which sentence from the excerpt best identifies the problem?

So they came by the thousands—kids, really, twenty-somethings, a few in their thirties.
But their goal was clear-cut, and that was enough.
No one knew for sure how to get to the moon, how to land, or get home.
That gave them purpose: a reason to puzzle out the problems and seek solutions rather than sleep.