Read the following passage and answer the questions (1-4)

Putting men on Mars has been an idea in science fiction for quite a while. However, when man first walked on the Moon, walking on Mars suddenly seemed feasible. A manned mission to Mars would be a huge milestone in space exploration. It would allow a more in-depth study of the Red Planet, and many have argued that building a permanent base on Mars is much more practical than building one on the Moon. A mission to Mars would be similar to the Moon landings, but much more difficult. The trip is about a hundred times longer, and there are new problems such as the Martian weather which must be considered. NASA currently has plans to have a man on Mars sometime in the 2030s, while the ESA plans to do so also around the same time. Russia has plans to launch a manned Mars mission by 2040.

Sending human beings to Mars has been a topic of —.