C. An irrational number is a number that, as a decimal, will never end. Ex. Pi, 4.13—- 1.9 is a real number, as it terminates, and it is exact. B and C simplified equal 7 and 6. Thus, C is the answer. Try and put that choice into your calculator, and see what the answer is. Then put the others in. What is the difference between the results? Hope it helps!!