It doesn't take a rocket scientist long time to figure out that there are better things yo

It doesn't take a rocket scientist long time to figure out that there are better things you could do for your health than take deep breaths on a smoggy（烟雾的）day. A growing pile of research suggests that even relatively low levels of air pollution may be more harmful than previously realized, to both heart and lungs(肺). The latest articles from researchers, published this week in the New England Journal of Medicine, focuses on how particulate (微粒) matter from air pollution affects lung function.
“The effect of low levels of particulate pollution found in many urban areas is not unlike secondhand smoke,” experts say. Studies show that short-term effects from particulates include diminished（减少） lung function, coughing, wheezing, and heart attacks. Long-term exposure can also slow normal lung growth, damage lung airways, and increase the risk of dying from lung cancer.
Certain populations, such as the very old and the very young, are the most vulnerable to air pollution. However, even the most alarming studies conducted in the most polluted areas suggest that the average person's individual risk from exposure (暴露) is very slight. Relative risk numbers often seem more frightening than they actually are. For example, an earlier study published in the New England Journal of Medicine found that short-term exposure to traffic fumes tripled ( 成为3倍) the risk of heart attacks in heart-attack survivors.
Short of moving to the countryside or at least away from busy roads, shielding yourself from the effects of air pollution is not easy. Masks won't work. “At the very least,” suggests Murray Mittleman, a cardiologist at Harvard University, “people who regularly exercise outdoors near highways may want to consider remapping their route.”
66. What does the underlined sentence in the first paragraph mean?
A. Rocket scientists are making researches on people’s health.
B. It's obvious that air pollution has a bad effect on people’s health.
C. People aren't sure whether taking deep breaths on a smoggy day is bad.
D. People often have a hard time when taking deep breaths on a smoggy day.
67. The word vulnerable in Paragraph 3 probably means     .
A. easy to be hurt            B. easy to be protected
C. easy to be used            D. easy to be saved
68. The main idea of Paragraph 3  is     .
A. that even small risk from particulate causes big problems
B. that air pollution often leads to heart attack
C. who are most likely to get affected
D. that we shouldn't worry about the average low risk
69. In order to be healthier, you'd better     .
A. take deep breaths         B. wear a mask   
C. live in a countryside       D. clean the busy road
70. The passage is written in a(n)      tone.
A. subjective         B. humorous     C. doubtful      D. objective66----70 BAACD