First of all
First,
the symbiotic association is so well-balanced that the roots of host plants show no damage even when densely infected. Second,
the fungi cannot as yet be cultivated in the absence of a living root.
Despite these difficulties, there
has been important new work that suggestsFrom above, no one said that the fungi CANNOT be cultivated in laboratory or study: the can't be reproduced if we do NOT have living root
It can be inferred from the passage that which of the following has been a factor influencing the extent to which research on mycorrhizal fungi has progressed?
(A) Lack of funding for such research
No money is mentioned
(B) Lack of immediate application of such research
We do have even though the scenario is not totally clear
(C) Lack of a method for identifying mycorrhizal fungi
See my explanation above
(D) Difficulties surrounding laboratory production of specimens for study
Correct
(E) Difficulties ensuing from the high cost and scarcity of superphosphate fertilizers
High cost and scarcity are not mentioned in the passage
20. The passage suggests which of the following about the increased resistance to harmful root fungi that some plants infected with mycorrhizal fungi seem to exhibit?
(A) There are at least three hypotheses that might account for the increase.
Correct. It is mentioned in the last sentence of the passage
(B) An explanation lies in the fact that mycorrhizal fungi increase more rapidly in number than harmful root fungi do.
More rapidly is not mentioned
(C) The plants that show increased resistance also exhibit improved nitrogen fixation.
We do not know. It is not addressed by the passage at all this dual possibiltiy
(D) Such increases may be independent of mycorrhizal infection.
I do not think so otherwise the entire passage would not exists
(E) It is unlikely that a satisfactory explanation can be found to account for the increase.
We do not know. We are investigating along with 3 main hypothesis
Hope this helps
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