Which of the following is the primary cause of thinning of the ozone layer?
a. gases composed of carbon, chlorine, and fluorine
b. coolants in refrigerators and air conditioners
c. chlorofluorocarbons
d. all of these choices
D
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Which of the following statements are true of a T cell that expresses two ? chains (and thus two different T-cell receptors) as a result of ineffective allelic exclusion of the ? chain during rearrangement? (Select all that apply.)
a. Engaging either of the T-cell receptors on MHC molecules of the thymic epithelium will result in positive selection. b. One of the T-cell receptors will be functional while the other will most probably be non-functional. c. If either T-cell receptor binds strongly to self-peptides presented by self-MHC molecules, the thymocyte will be negatively selected. d. One of the T-cell receptors may be autoreactive but escape negative selection because its peptide antigen is present in tissues other than the thymus. e. Subsequent gene rearrangements may give rise to a ?:? T-cell receptor.
Rodlike structures within the nucleus are:
The Education for All Handicapped Children Act was first passed by Congress in 1994
Indicate whether the statement is true or false
An infection of the female reproductive tract that can result from an untreated sexually transmitted infection is known as what?
A) Pelvic inflammatory disease B) Gonorrhea C) Human papillomavirus D) Dormant herpes