In the trp operon, tryptophan serves as a(n) , binding to the repressor and causing it to block to attachment of RNA polymerase. a. operator
b. inducer
c. repressor
d. corepressor
e. gene

The answer is A

High tryptophan: The tryptophan binds to the trp repressor and causes it to change shape, converting into its active (DNA-binding) form. The trp repressor with the bound tryptophan attaches to the operator, blocking RNA polymerase from binding to the promoter and preventing transcription of the operon.

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.