A. Doesn't matter where the amino acid is present or produced.
B. May be decline in other amino acids can allow the herb to grow. This actually weakens.
D. This in fact helps the herb to adapt and thus no need of amino acid.
E. After some time the metals become inert because of excessive amino acid. Once metal becomes inert then no further need of amino acid. This strengthens.
C. This tells that others too grow because of high amino acid production and this strengthens in a better way.
I will go with C. E, though strengthens, but raises a lot of questions.