On the area-amplitude ultrasonic standard test blocks, the flat-bottomed holes in the
blocks are:
(a) All of the same diameter
(b) Different in diameter, increasing by 1/64 inch increments from the No. I block
to the No. 8 block
(c) Largest in the No. I block and smallest in the No.8 block
(d) Drilled to different depths from the front surface of the test block