Choose the word or phrase among A, B, C or D that best fits the blank space in the following passage.
Gravity and weightlessness
Our everyday lives (36) such activities as sitting, walking, picking up things from the ground and lying in bed. None of these activities are possible in orbit.
(37) a spacecraft reaches orbit, everything inside it seems to be weightless. Anything or anyone that is not tied down will float. Weightlessness allows astronauts to appear very (38) . They can lift objects that would be (39) heavy to move on Earth. But there are some drawbacks.
(40) the effect of gravity, blood and other body fluids begin to flow towards the head. This can cause a feeling of headaches. With no gravity to push against, bones and muscles can become weak. To (41) fit, they have to exercise several hours each day. This allows them to recover more quickly when they (42) to Earth.
In a space shuttle or space station, there is no up or down. There is no difference (43) a floor and a ceiling. This can make astronauts feel (44) until they get used to this strange (45) .

Read the passage, and choose the correct answer A, B, C or D for each question.
SETI: The Dream of Life in Space
People have always gazed up at the stars in wonder. Their imaginations are filled with possibility as they think carefully how large the universe is and whether or not we are alone in it. Of all the stars out there, are there intelligent beings on a planet circling one of the stars looking back at us and wondering the same thing?
It is difficult to comprehend how many stars there are, or even to guess the possibilities of their being intelligent life. Yet our interest in finding out is so strong that the search has been going on for over a century. What we consider the modem Search for Extraterrestrial Intelligence (SETI) began around 1960.
The SETI project not what many people think it is. A simple explanation is that scientists study electromagnetic waves that are being emitted throughout the universe. When they are looking at these waves, they have a good idea of what are considered natural, random patterns the waves take. Therefore, they are searching for anything that does not appear to be randomly. If they were able to find something non-random, they would believe that an intelligent source of some kind must be creating it. In other words, intelligent life would have to exist somewhere else in the universe.
While the SETI project will continue to listen for signals from intelligent sources, other progammes hope to find any source of life. The Mars rovers will continue to search for dry lake beds and other areas on the Red Planet that may have once held life. If any life can be found outside the earth, then we are probably on our way to finding life that could be similar to our own.