Lactose is a disaccharide of

Read the given statements.
i. Fructose is the sweetest sugar.
ii. Glycine is the simplest amino acid.
iii. Lactose is a disaccharide composed of one molecule each of glucose and galactose.
iv. Cellulose is an unbranched chain of glucose molecules linked by $\beta$1, 4-glycosidic bond.
Which of the given statements are correct?

A sample of an enzyme called lactase was isolated from the intestinal lining of a calf. Assays were undertaken to evaluate the activity of the enzyme sample.

The substrate of lactase is the disaccharide lactose. Lactase breaks a lactose molecule in two, producing a glucose molecule and a galactose molecule. Two assays were carried out.

Assay 2

Lactose concentration (% w/v)	0	5	15	20	25	30
Concentration of enzyme sample(% v/v)	5	5	5	5	5	5
Reaction rate ($\mu$ mole glucose $se{c}^{-1}m{L}^{-1}$)	0	15	25	35	40	40

What are the variables in each of the two assays?