smc

From the problem we can set the altitude equal to $a$, the shorter base equal to $a-d$, and the longer base equal to $a+d$. By the formula for the area of a trapezoid, we have $K=a^2$. However, since $a$ can equal any real number $(3,2.7,\pi )$, none of the statements $A,B,C,D$ need to be true, so the answer is $\boxed{\text{taken alone neither}\text{(A)}\text{nor}\text{(B)}\text{nor}\text{(C)}\text{nor}\text{(D)}\text{is true}}$.