GMAT Critical Reasoning (CR) | Re: Most homeowners' efforts to rid their gardens of dandelions depend

You are given that the ratio of young to old is 20:1, so you don't need to know the percentage.

However, I am confused on why it's not B. The artificial killers only kill adult weeds and not younger weeds, so wouldn't you need to know the time frame for whatever juvenile weeds are left to mature so that you can kill them off before they reproduce? I thought this was better than E because all of the dandelions are not the same age
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