main casing

例句：

1. 1.The main casing of the machine is made of steel.
   这台机器的主体是由钢制成的。
2. 2.The main casing of the ship is made of wood.
   船的主体是由木头制成的。
3. 3. The main casing of the car is made of aluminum.
   汽车的主体是由铝制成的。