BEING an astronaut sounds cool, doesn't it? In space, they get to do some pretty amazing things, like floating in zero gravity(重力).
However, there are also plenty of things that astronauts can't do because of their weightless environment, and that's very sad. What's worse, they can't even let their sadness show, because it's impossible to cry in zero gravity.
Of course, astronauts can still produce tears. But crying is much more difficult in space, according to The Atlantic(大西洋月刊) in January. Without gravity, tears don't flow(流动) down out of the eyes like they do here on Earth. This means that when you cry in space, your tears have nowhere to go-they just stick(粘) to your eyes.
In May 2011, astronaut Andrew Feustel experienced this during one of his spacewalks. "Tears," he said, "don't fall off of your eyes...They just kind of stay there."
Besides making your vision(视线)unclear, this can also cause physical pain. Back on Earth, tears are supposed to bring comfort to the eyes. But that's not the case in space. The space environment dries out astronauts' eyes, and when tears suddenly wet the eyes, it can cause pain rather than comfort. "My right eye is stinging(刺痛) like crazy," Feustel told his teammate during the walk.
Since gravity doesn't work in space, astronauts need some extra help to get rid of（除去） the tears. Feustel chose to rub his eyes against his helmet to wipe(擦) the tears away. Another choice is to just wait-"When the tears get big enough they simply break free of the eyes and float around," astronaut Ron Parise told The Atlantic.
There are lots of small things-things like crying-that we are so used to on Earth. We usually take them for granted until they become a problem in a totally different environment, like space.  There, astronauts can't talk to each other directly. They also can't eat or drink in normal ways. They can't even burp (打嗝), because there is no gravity to hold the food down in their stomach. If they do burp, they just end up throwing up（呕吐）everything in their stomach, according to the UK National Space Center.
Therefore, perhaps it's only space explorers who can honestly say: "Gravity, you're the best."
From Paragraphs 2 and 3 , we can know that_______.

A．astronauts are unable to feel sad in space

B．astronauts produce fewer tears in space

C．tears produced in space flow down more slowly

D．tears produced in space don't flow downward

What effect do tears have on astronauts?

A．They cause physical pain.

B．They bring comfort to them.

C．They make their vision clearer.

D．They float around and cause trouble.

The underlined phrase "take them for granted" in paragraph 7 means _______.

A．find them important

B．consider them useless

C．need them during an emergency

D．fail to notice their presence(存在)

The second-to-last paragraph (paragraph 7) is mainly about_______.

A．suggestions of how astronauts can stay comfortable in space

B．other basic things that are difficult to do in space

C．why burping is impossible in space

D．things human can't do without gravity