Given below are two statements: One is labeled as Assertion (A) and the other is labeled as Reason (R).

Assertion (A) : ATP is used at two steps in glycolysis.

Reason (R) : The first ATP is used in converting glucose into glucose-6-phosphate and second ATP is used in the conversion of fructose- 6-phosphate into fructose-1-6- diphosphate.

In light of the above statements, choose the most appropriate answer from the options given below.

Assertion (A) is true. In glycolysis, which is the metabolic pathway that converts glucose into pyruvate, two ATP molecules are used at specific steps. 

Reason (R) is also true. During glycolysis, glucose is converted into pyruvate, which involves a series of enzymatic reactions. The first step of glycolysis is the conversion of glucose to glucose-6-phosphate, which is catalyzed by the enzyme hexokinase and requires the input of one molecule of ATP. The second step involves the conversion of fructose-6-phosphate to fructose-1,6- bisphosphate, which is catalyzed by the
Enzyme phosphofructokinase and also requires the input of one molecule of ATP. 

Thus, ATP is used at two steps in glycolysis: once in the conversion of glucose to glucose-6-phosphate and once in the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate.

 Both A and R are true and R is the correct explanation of A.