还可以用尖嘴器具敲击板材表面，如果生意差异较大，就说明内部有空洞。
Jianzui apparatus can also use percussion sheet surface, if the difference between larger business, the internal cavity.
还可以用尖嘴器具敲击板材表面，如果生意差异较大，就说明内部有空洞。
Jianzui apparatus can also use percussion sheet surface, if the difference between larger business, the internal cavity.
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