Answer:
C. repressible
Explanation:
The trp operon in bacteria is a repressible operon. The regulatory gene codes for repressor protein. In the presence of tryptophan, the repressor (inactive) binds with tryptophan and gets activated. This active repressor attaches with operator and prevent polymerase to bind and thus inhibiting transcription of genes in the operon.
The mutant strain cannot attach to operator (trpO+) but it can make dimers. As the operator is mutated so it prevent binding of repressor to operator. Thus, expression of the trp operon is repressible.
