至于内包装,必须有吸引力和有助于销售,外包装必须适合海运。可以翻译为:As to the inner packing, it must be strong enough to stand shock and rough handling and the outer packing must be seaworthy.
【单选题】A person pulls a box along the ground at a constant speed. If we consider Earth and the box as our system, what can we say about the net external force on the system?
A.
It is zero because the system is isolated.
B.
It is nonzero because the system is not isolated.
C.
It is zero even though the system is not isolated.