It is thought that crying is hardly an activity encouraged by society. Tear, whether they are of sorrow, anger, or joy, typically make Americans feel uncomfortable and embarrassed. The shedder of tears (落泪者) is likely to apologize, even when a great tragedy was the cause. The observer of tears is likely to do everything possible to put an end to the emotional tears. But judging from recent studies of crying behavior, both those responses to tears are often inappropriate and may even be counterproductive (适得其反).
Humans are the only animals clearly known to shed emotional tears. Since evolution has given rise to few purposeless physiological responses, it is logical to assume that crying has one or more functions that enhance (increase) survival.
Although some observers have suggested that crying is a way to ask for assistance form others (as a crying baby might from its mother), the shedding of tears is hardly necessary to get help. Vocal cries would have been quite enough, more likely than tears to gain attention. So, it appears, there must be something special about tears themselves.
Indeed, the new studies suggest that emotional tears may play a direct role in alleviating stress, University of Minnesota researchers who are studying the chemical composition of tears have recently isolated two important chemicals from emotional tears. Both chemicals are found only in tears that are shed in response to emotion. Tears shed because of exposure to cut onion would contain no such substance.
Other researchers are investigating the usefulness of tears as a means of diagnosing human ills and monitoring drugs. At Tulane University’s Teat Analysis Laboratory Dr. Peter Kastl and his colleagues report that they can use tears to detect drug abuse, to study the causes of “dry eye” syndrome（综合症）and the effects of eye surgery, and perhaps even to measure exposure to environmental pollutants.
What does the phrase “both those responses” in Paragraph 1 refer to ?

A．Crying out of sorrow and shedding tears for happiness.

B．The embarrassment and unpleasant sensation of the observers.

C．The tear shedder’s apology and the observer’s effort to stop the crying.

D．Linking illness with crying and finding the chemical composition of tears.

From the passage we can infer that        .

A．it is unnatural for people to shed tears

B．we can reduce our stress by shedding tears

C．shedders of tears can’t get help by crying loudly

D．unlike animals, humans can shed tears for survival

What does the passage mainly talk about?

A．Roles of emotional tears.

B．functions of shedding tears.

C．Unwelcome shedders of tears.

D．Research on the effects of tears.