Answer:
C. Finding a solution to kudzu took a long time.
Step-by-step explanation:
According to the given excerpt, it is stated that the kudzu plants help to prevent erosion but also helps to block other vegetation from receiving adequate sunlight because they grow over them.
Because of this, researchers spent many years in research before finding a herbicide that would make the kudzu grow better.
From paragraph 3, it can be inferred that finding solution to the kudzu took a long time.