单项选择题

The primary purpose of the passage is to

(A) contend that key terms in a scientific theory have been improperly used
(B) argue that proponents of a scientific theory have obscured important details
(C) demonstrate that two views once thought to be in conflict are actually identical
(D) suggest that proponents of a theory have not stated their data in an exhaustive manner
(E) show that a theory has been drawn into question by a more recent study

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单项选择题

The passage mentions that at various points, scientists have believed all of the following to be essential for the nitrogen fixation process EXCEPT

(A) The presence of ammonia
(B) The permeability of cell membranes
(C) The presence of rhizobia
(D) The synthesis of amino acids
(E) Nitrogen-containing molecules like nucleotides

单项选择题

It can be inferred from the passage that scientists are perplexed by the means (line 12) for which of the following reasons

(A) They are unsure of how alanine remains separate from the everyday nitrogen metabolism of the plant itself.
(B) They have yet to establish what function the alanine serves for the soybean plants.
(C) They have thought alanine to exist only in very small quanties in rhizobia.
(D) They have long considered the membranes of the soybean plant impermeable to amino acids.
(E) They are uncertain how such a rapid export of fixed nitrogen is possible through the soybean membranes.