According to the author, what is the main reason space exploration is so costly?

The main costs of space exploration arise from the fact that we are set on sending humans, rather than robots. The reasons such efforts drive up the costs include: A human needs a return ticket, while a robot can go one way. And they can do most tasks humans can.

the president has the power to appoint federal judges, ambassadors, and other "principal officers” of the united states, subject to senate confirmation of such appointments.

answer///conference committee;