Which of following statement is true for lac operon in E-coli
(a) lac operon consists of one regulatory gene and five structural gene.
(b) The i gene codes for inducer
(c) The z-gene codes for `beta` -galacosidase
(d) A very low level of expression of lac operon has to be present in cell all the time

Options

A. a, b, c, d
B. a, c, d
C. c, d
D. b, d

Answer

To solve the question regarding the lac operon in E. coli, we need to analyze each of the provided statements one by one.

### Step-by-Step Solution:

1. **Statement (a): "lac operon consists of one regulatory gene and five structural genes."**
- The lac operon actually consists of one regulatory gene (the i gene) and three structural genes (z, y, and a). Therefore, this statement is **false**.

2. **Statement (b): "The i gene codes for inducer."**
- The i gene does not code for the inducer; instead, it codes for the repressor protein that inhibits the operon. The actual inducer is lactose. Thus, this statement is **false**.

3. **Statement (c): "The z-gene codes for beta-galactosidase."**
- The z gene indeed codes for the enzyme beta-galactosidase, which is responsible for breaking down lactose into glucose and galactose. Therefore, this statement is **true**.

4. **Statement (d): "A very low level of expression of lac operon has to be present in cell all the time."**
- It is true that a low level of expression of the lac operon is maintained at all times to ensure that the cell can respond quickly to the presence of lactose. Hence, this statement is **true**.

### Conclusion:
The true statements regarding the lac operon in E. coli are:
- Statement (c) is true: "The z-gene codes for beta-galactosidase."
- Statement (d) is also true: "A very low level of expression of lac operon has to be present in cell all the time."

### Final Answer:
The correct answer is that statements (c) and (d) are true.

---