What is measured when taking blood pressure?

Lactose present, glucose absent.

Explanation:

Lac operon may be defined as a cluster of genes that regulate the metabolism of lactose in bacteria. The bacteria always prefer glucose if both glucose and lactose is present in the medium.

The conditions that causes the maximal expression of lactose is the presence of lactose and absence of glucose. This is due to the action of catabolite activator protein and cyclicAMP.

Thus, the correct answer is option (1).