Which sentence represents a quadratic equation that can be expressed in standard form?
a) a number squared is equal to the sum of zero and the same number squared.

b) there are here consecutive even integers such that one third the sum of the greater two is equal to the least of the three.

c) the square of the difference between a number and one is thirty-six

d) one divided by a number is equal to one divided by the sum of twice the number and one.