单项选择题

How any fetus survives gestation has baffled scientists for decades: the embryo’s tissues are half foreign and yet, unlike______organ transplant, it isn’t normally rejected.

(A) an adaptive
(B) a mismatched
(C) a successful
(D) an obdurate
(E) a preplanned

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单项选择题

Real body fluids, like those between our ceils, are less______than the model fluids that the researchers have used so far, and thus may introduce complications.

(A) experimental
(B) tested
(C) numerous
(D) unresponsive
(E) foreboding

单项选择题

In contemporary usage, continents are understood to be large, continuous, ______ masses of land, for they are almost always separated by expanses of water.

(A) elevated
(B) arable
(C) identified
(D) irregular
(E) discrete

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