T cells that undergo positive and negative selection ensure that
a. mature T cells only react strongly with foreign antigens.
b. mature T cells react with foreign and self antigens.
c. mature T cells react strongly with foreign antigens or do not react at all.
d. mature T cells react strongly with self antigens.
Answer: A
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An autoimmune disease occurs when:
A. immune cells react too strongly with antigens normally present on host cells. B. there is an unregulated release of cytokine by helper T cells. C. cytotoxic T cells attack B cells. D. macrophages engulf normal host cells.
The most abundant group of seedless tracheophyte plants are the
A. club mosses. B. horse tails. C. angiosperms. D. ferns. E. gymnosperms.
The bile from the liver
A. contains enzymes. B. is stored in the pancreas. C. emulsifies fats. D. is emptied into the stomach.
Which of the following is not a characteristic of species?
A. Geographic isolation B. Ability to produce fertile progeny C. Different number of chromosomes between individuals D. Common evolutionary ancestry E. Shared characteristics such as shape, size, and color (in individuals of the same life stage and sex)