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Osteoporosis is a disease that reduces bone mass, leading to fragile bones that break easily. Current treat- ments for osteoporosis such as estrogen or calcitonin help prevent further loss of bone but do not increase bone mass. Since fluoride is known to increase bone mass, administering fluoride to osteoporosis patients would therefore help make their bones less susceptible to breaking.

Which of the following, if true, most seriously weakens the argument above?

A．{{*HTML*}}Most people who suffer from osteoporosis are not aware that administration of fluoride can increase bone mass.
B．{{*HTML*}}Fluoride is added to drinking water in many locations in order to strengthen the teeth of people who drink the water.
C．{{*HTML*}}The risk of contracting osteoporosis and other degenerative bone diseases is lessened by exer- cise and an adequate intake of calcium.
D．{{*HTML*}}Unlike administration of fluoride, administration of estrogen or calcitonin is known to cause undesirable side effects for many people
E．{{*HTML*}}The new bone mass that is added by the administration of fluoride is more brittle and less elastic than normal bone tissue.