harpott is absolutely right. E needs to say "a single strain" to be valid. (This doesn't change the appositive relationship between "a practice" and "the use," since the phrase in question is part of a modifier.)
To be clear, we can say "the use of one strain," but throwing in an adjective such as "single" necessitates an article ("a").
Incorrect: The gift of green sweater was appreciated.
Correct: The gift of a green sweater was appreciated.
...
To be clear, we can say "the use of one strain," but throwing in an adjective such as "single" necessitates an article ("a").
Incorrect: The gift of green sweater was appreciated.
Correct: The gift of a green sweater was appreciated.
...
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