It is generally believed that we are getting cleaned when we step under a shower. We are, but we’re also giving a home to lots of tiny little creatures we didn’t even know about. A showerhead carries thousands of bacteria called Mycobacterium．These can cause problems like coughs and tiredness, and a general feeling of poorliness (身体不舒服). When you turn on the water, the bacteria go from the showerhead onto and into your body.
This is a finding of Norman R. Pace and his team at the University of Colorado, in the US. The scientists investigated bacteria in all kinds of human environment, including showers．Pace's team looked at 45 showerheads in nine American cities. They discovered that 30 percent of them had large amounts of flying Mycobacterium.
But Pace said that they pose few threats to the health．Only those with a weak immune system might need to worry．He told the New York Times that the bacteria are not as unpleasant as might be thought．He said that having a shower is no more dangerous than anything else we do in the morning．
But for those who feel sick about the idea of all those microorganisms (微生物), he had some advice. Let the water run for 30 seconds before getting into the shower. Why? The number of bacteria is smaller than that when the water is just turned on. If that seems like a waste of water, he added that you could also change your showerhead every few months.
However, Pace had good news too. He has also been testing the air in US subways. Apart from iron particles (粒子), which are ground off the track by the wheels of trains, subway air is fresh. The reason is that a train’s movement pumps fresh outdoor air into the tunnels.
Pace explained that he wanted to understand the natural microbial environments of public places. This kind of knowledge might help discover the microbes to be used in a bioterrorist (生物恐怖分子) attack.
From the finding of Norman R. Pace, after taking a shower, we might cough or feel tired because      .

A．it’s easy to get a cold when taking a bath

B．the showerhead carries many bacteria causing illness

C．we don’t get cleaned while showering

D．we don’t get a weak immune system

According to the passage, which of the following is TRUE?

A．Hot water could kill most of bacteria in showerheads.

B．Of 45 showerheads surveyed in nine cities, 30 carried large amounts of Mycobacterium.

C．Changing showerheads is the only way to avoid microorganisms.

D．Shower water contains much less bacteria after being left to run for 30 seconds.

We can learn from the third paragraph that       .

A．having a shower in the morning is more dangerous than at other time

B．the bacteria always threat people’s health

C．there is no reason to fear microorganisms for people with strong immune system

D．it is better to do some exercise in the morning than have a shower

The underlined word “pose” in the third paragraph probably means “______”．

A．cause

B．avoid

C．describe

D．promise

What contributes to fresh air in US subways?

A．The train’s movement.	B．Iron particles．
C．Train wheels.	D．Air conditioners on the trains．