Many millions of people have high blood pressure(hypertension 高血压). What's so frightening about this so called silent killer is that it often does not produce (51) for years, secretly damaging arteries and organs throughout the body until it erupts (爆发) in the form. of stroke, heart attack, congestive heart failure(充血性尽力衰竭) or kidney disease. (52) left untreated, even mild hypertension can reduce the life expectancy of a 35-year-old (53) several years. (Readings of 140 to 159 over 90 to 99 are mildly high; about 120/80 is normal. )
That's why high blood pressure is commonly treated with anti-hypertensive drugs. But studies (54) that in some people an increase in calcium(钙) consumption can help (55) blood pressure without medication(药物治疗)。
Calcium also seems to help prevent high blood pressure. (56) the results of 13-year survey (57) by the U.S. National Center for Health Statistics, James H. Dwyer, associate professor of (58) medicine at the University of Southern California School of Medicine, found that people who consumed 1300 milligrams of calcium a day were 12 percent (59) likely to develop hypertension than those (60) only 300 mg. a day. In people under age 40, risk was reduced by up to 25 percent.
Soon doctors may (61) some hypertension patients to increase their calcium intake, (62) the way they now advise sodium(钠) restriction. "It's (63) to add food or supplements than to go on a low-sodium diet," (64) Dr. David McCarron, professor of medicine at Oregon Health Sciences University. "Our studies show that people who try the low-sodium (65) don't stay with it very long. "
(51)

A. evidence
B. symptoms
C. marks
D. sign