72÷6×5=____ 2×(15-7)=____ 51÷(17-14)=____ 54 –(13+18)=____
62-32 ÷4 =____ 25-8 ×2 =____ 8×2÷4 =____ 35-10 +26 =____
8×9÷6=____ 68+32-49 =____ 3×8÷6=____
板块构造学说认为,几乎全部是海洋的板块是( )