21.   Calcium absorption -- crucial to building and maintaining bone mass -- is linked to estrogen, and slows after menopause when the levels of the naturally occurring estrogen drop.

22.   Check the sight glass weekly and add water whenever the level drops.

23.   Construction of the pipeline comes at an especially sensitive time, as temperatures around the state inch up and aquifer levels steadily drop.

24.   Consistent with this view, Flier finds that leptin levels drop when people are losing weight.

25.   During menstruation, hormone levels drop as does the risk for knee injuries.

26.   During the first few sessions, he was unable to arrive at what had caused his performance level to drop.

27.   Especially at risk are men whose testosterone levels drop significantly in their later years and those who have androgen-blocking treatment for prostate cancer.

28.   He said the snow level should drop to the level of Lake Tahoe by the end of the week.

29.   If antibody levels drop suddenly, the coach is advised to ease up on the training program.

30.   If both ovaries are removed surgically from a premenopausal woman, her testosterone level will drop by a third or more.