Answer:
Option C is independent variable.
Step-by-step explanation:
Independent variables are those where one entity does not depend on the other or the change in one does not cause changes in other.
A. how fast you write and how fast you finish your assignment - this is dependent variable as the speed to finish your assignment is dependent on the speed of your writing.
B. your electricity consumption and your electricity bill - this is dependent as the more the electricity consumption, the more is electricity bill.
C. your electricity bill and your age - This is independent as the bill is not based on someones age.
D. how fast you read and the time it takes you to finish a book - This is dependent as the more fast you read, the more early you can finish reading the book.
E. your monthly income and your monthly expenditures - This is dependent as the more the income, more expenditure can be afforded.