Answer: Options BCG
The operon is usually open,the active repressor binds to the operator to stop transcription and it is found in prokaryotes.
Step-by-step explanation:
Trp operon are group of genes that can encode biosynthetic enzymes to produce tryptophan. They are found in E.coli a prokaryotes and are usually open. Trp operon is turned on when tryptophan levels are low and turned off when they are high.
It is regulated such that when tryptophan gene is available in the environment,the genes for tryptophan synthesis are not expressed. The active reprossor binds the promoter to stop transcription. It is regulated by tryptophan repressors.