When checking tires, finding which of the following is not a cause for concern?

When checking your vehicle's tires, you should confirm that air pressure is neither too low nor too high; that there is at least 4/32 of an inch of tread depth in every major groove on the front tires; that there is at least 2/32 of an inch of tread depth in grooves on other tires; and that radial and bias-ply tires are not used together.