Astronauts in space cannot stand erect this is because in space

The correct answer is (a). There is no gravity in space.

(b) is incorrect because viscous forces are not strong enough to prevent astronauts from standing erect.
(c) is incorrect because the solar wind is a stream of charged particles from the sun, and it does not exert an upward force on astronauts.
(d) is incorrect because atmospheric pressure is very low in space, but it is not strong enough to prevent astronauts from standing erect.

In space, there is no gravity to pull astronauts down. This means that they can float freely in the air. They can also move around by pushing off of objects or by using their jetpacks.