题目内容：
Natural MedicineSince earliest days，humans have used some kinds of medicines．We know this because humans have survived．Ancient treatments for injury and disease were successful enough to keep humans from dying out completely．
They were successful long before the time of modem medicine．Before the time of doctors with white coats and shiny(发亮的)instruments．Before the time of big hospitals with strange and wonderful equipment．
Many parts of the world still do not have university—educated doctors．Nor do they have expensive hospitals．Yet injuries are treated．And diseases are often cured,how?By ancient methods．By medicines that might seem mysterious，even magical(有魔力的)．Traditional medicines are neither mysterious nor magical，however．
Through the centuries，tribal(部落的)medicine men experimented with plants．They found many useful chemicals in the plants．And scientists believe many of these traditional medicines may provide the cure for some of today’s’most serious diseases．
Experts say almost 80％of the people in the world use plants for health care．These natural medicines are used not just because people have no other form of treatment．They are used because people trust them．In developed areas，few people think about the source of the medicines they buy in a store．Yet many widely—used medicines are from ancient sources， especially plants．Some experts say more than 25％of modem medicines come，in one way or another，from nature．
Scientists have long known that nature is really a chemical factory．All living things contain chemicals that help them survive．So scientists’interest in traditional medicine is not new．But it has become an urgent concern．This is because the earth’s supply of natural medicines may be dropping rapidly．
根据以上内容，回答题。
The passage indicates that ancient treatments for injury and disease were______． A．much more successful than modern ones
B．successful in all cases
C．successful enough for humans to survive
D．of little help to humans
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