A.4mm B.6mm C.8mm D.30mm
A.2 B.3 C.5 D.6
A.從低處砌起,并應(yīng)由高處向低處搭砌 B.從低處砌起,并應(yīng)由低處向高處搭砌 C.從高處砌起,并應(yīng)由高處向低處搭砌 D.從高處砌起,并應(yīng)由低處向高處搭砌