D
Tears are nature's way of making us feel more comfortable. When our eyes is made uncomfortable by some small pieces of pollution, or when we are cutting onions, or when we are exhausted and “red –eyes” from over work and late hours, tears form in our eyes to clean and re-flesh them.
Tears are also a sign of strong emotion. We cry when we are sad and we cry when we are happy.
And tears seem to be uniquely（唯独）human. We know that animals also experience emotion—fear, pleasure, loneliness — but they do not shed （流） tears. From this, we can conclude that tears are closely related to the emotional and biological make up of the human species.
Biologically speaking, tears are actually drops of saline fluid, which is a little bit salty, produced by a gland（腺）in the body. Because salt is an important component, tears may actually constitute the most conclusive evidence that the human animal is the end product of a long evolutionary process that began in the sea.
And it is clear that, in addition to（除了） the emotional benefits（好处）, the shedding of tears has a specific biological function as well. Through tears, we can eliminate from our body certain chemicals which build up in response to stress and create a chemical imbalance in the body. Crying actually makes us feel better by correcting that imbalance and making us feel good again. And thus the emotional and the biological functions of tears merge（合并）into one and make us even more "human" than we would otherwise be.
68．According to the passage, human beings may have originated（起源于）in________.
A．the sea B．the salt C．chemicals D．animals
69．Which of the following is NOT a function of tears?
A．Biological B．Emotional C．Political D．Chemical
70．According to the article, which of the following is unique to humans?
A．The feeling of loneliness. B．The state of feeling good.
C．The ability to shed tears D．The feeling of fear
71．The underlined word “eliminate” probably means_______.
A．add B．produce C．replace D．remove