Choose the biconditional statement with the same meaning as these two statements combined:
statement 1: if a number is positive, then it is greater than zero.
statement 2: if a number is greater than zero, then it is positive.
select one:
a. a number is positive if and only if it is not zero.
b. if a number is positive and greater than zero, then it is not negative.
c. if a number is non-negative, then it is positive.
d. a number is positive if and only if it is greater than zero.