单选题 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.
B、 Lack of immediate application of such research.
C、 Difficulties surrounding laboratory production of specimens for study.
D、 Lack of a method for identifying mycorrhizal fungi.

【正确答案】 C

【答案解析】文中提到两个原因，其中第二个原因“the fungi cannot as yet be cultivated in the absence of a living root”(不能在缺乏根的环境下独立培养真菌)与C项(实验室培养的困难)意思一致。A，B，D均不正确。