单项选择题 Provision must be made in pipe systems for changes in length due to change of temperatureThe bold and italic word “provision” probably means （）.

单项选择题 Cast iron and gunmetal fittings are used freely in small sizes at moderate pressure; large fittings, those for high pressure and temperature are cast or mild steelIn the above sentence, the word “those” means （）.

单项选择题 Wrought iron has an inherent resistance to corrosion but is not to be had freely , its place has been taken by the cuprous alloysAccording to the above sentence , which of the following statements is true?（）