Scientists have long been looking for life in outer space. They recently found something exciting _______ Venus(金星), the planet closest to ours.

British scientists _______ phosphine gas(磷化氢) in Venus’ atmosphere(大气层) already. Phosphine is a promising sign of life. On Earth, phosphine is produced when organic(有机的) matter breaks down. The same thing could be _______ on Venus. Still _______ need to send a probe( 探测器) to Venus to see _______ life exists there.

In fact, Venus has long been ignored(忽视) in the search for life because of its ______temperatures and atmospheric pressure. Venus is the _______ planet in the solar system. Its surface temperature is 470℃, which is hot enough to melt spacecraft. The pressure there is 92 times greater than that on Earth. Even if humans could bear the heat, they would be crushed(粉碎) by the pressure.

However, it’s possible that life could exist in the planet’s atmosphere. Temperatures there are about -1℃ to 93℃，which is far more suitable _______ life. The pressure there is similar to that of Earth as well. The phosphine was found in Venus’ cloudy atmosphere-around 60 _______ above its surface.

Phosphine is known as an indirect sign of life. So are gases like methane and ozone(臭氧). Scientists focus on such signs when they look for ________ outside of Earth. These gases can exist in the atmospheres of planets for a long time allowing scientists to find them with the help of telescopes and probes. However, it is liquid water that is considered to be the most important sign of life.