Most plants can make their own food from sunlight,【C1】______ some have discovered that stealing is an easier way to live. Thousands of plant species get by【C2】______ photosynthesizing (光合作用), and over 4:00 of these species seem to live by pilfering sugars from an underground【C3】______ of fungi(真菌). But【C4】______ in a handful of these plants has this modus operandi been traced to a relatively obscure fungus. To find out how【C5】______ are【C6】 ______ , mycologist Martin Bidartondo of the University of California at Berkeley and his team looked in their roots. What they found were【C7】______ of a common fungus, so【C8】______ that it is found in nearly 70 percent of all plants. The presence of 'this common fungus in these plants not only【C9】______ at how they survive, says Bidartondo, but also suggests that many ordinary plants might prosper from a little looting, too.
Plants have【C10】______ relations to get what they need to survive. Normal【C11】______ plants can make their own carbohydrates through photosynthesis, but they still need minerals. Most plants have【C12】______ a symbiotic relationship with a【C13】______ network of what are called mycorrhizal fungi, which lies beneath the forest【C14】______ . The fungi help green plants absorb minerals through their roots, and【C15】______ , the plants normally【C16】______ the fungi with sugars, or carbon. With a number of plants sharing the same fungal web, it was perhaps【C17】______ that a few cheaters —dubbed epiparasites-- would evolve to beat the system.【C18】______ , these plants reversed the flow of carbons【C19】______ it into their roots from the fungi【C20】______ releasing it as "payment".
【C1】

A. but
B. if
C. because
D. though