C．exciting D．discouraging

　　解析：选D　在漫长的旅途之中，看到前面还有那么远的路要走，当然会使人感到气馁。

　　20．A.ever B．always

　　C．seldom D．frequently

　　解析：选C　事情是慢慢做完的，我们很少能一下子完成一件重大的事情。

　　Ⅱ.阅读理解

　　There are usually few things people want to do less than housework. But while washing the dishes and dusting the shelves seem like troublesome things, a new study has found just how important they are to our general health and happiness.

　　In fact, scientists now believe cleaning the house is more important to mental and physical health than other factors, such as the area you live in or how much you earn. Researchers at Case Western Reserve University say doing housework is helpful because of the exercise it takes to get the daily job done, which in turn affects mental health.

　　Dr. Kathy Wright and a research team at the university's Frances Payne Bolton School of Nursing wanted to find out how property (财产), education, environment and health behaviors, like smoking, affect an older person's health. The study's 337 participants, from 65 to 94 years old, had to have at least one chronic (慢性的) illness which prevented them from doing at least one basic daily task, such as bathing and dressing.

　　Dr. Wright said she was surprised to learn that doing housework and keeping their property affected the participants' mental and physical health more than other factors. "House cleaning kept them up and moving，" said Dr. Wright. "A clean environment is helpful in treating some illnesses. And poverty (贫穷) did not directly affect mental or physical health."

　　The study proved what Dr. Wright had observed in her visits: people living in a dirty environment seemed less satisfied than those in a place that was neat and tidy. Dr. Wright hopes the study shows how important it is for older people with chronic illnesses to continue physical activities, such as doing reaching exercises while sitting, standing up and sitting down in a chair.