What's the author's tone in the last sentence of the passage

A．The biggest hurdle for the space-tourism project is lack of a life supporting system.
B．The entrepreneurs trying to explore the space-tourism have plenty of money.
C．The government has little interests in this project.
D．The first passenger countdowns are within a few years.

A．Take Vacations in Space
B．Building Hotels in Space
C．Flight Regulations in Space Travels
D．Cost of Space Traveling