硬到硬
hard to───难于
hard───adj.努力的；硬的；困难的；辛苦的；确实的；严厉的；猛烈的；冷酷无情的；n.（Hard）人名；(英、芬、瑞典)哈德；adv.努力地; 猛力地; 严重地; 沉重地；adv.努力地；困难地；辛苦地；接近地；猛烈地；牢固地；adj.困难的; 硬的; 有力的; 努力的
hard wearing hard───耐磨的
hard by hard───一点一点地
play hard work hard───放肆玩乐，拼命工作
hard to bear───够受的
hard to know───很难知道
hard to answer───很难回答
hard to play───很难玩
Think of the fact, what circuitous tactics are not hard to hard.───想想事实上的迂回战术吧，什么事情都不要硬对硬地交锋。
Xiao Wang not only works hard, but (also) studies hard. His behaviour leaves nothing to be desired.───小王既肯干又肯学，真是没说的。
Real world friends are hard to find and hard to change.───现实中的朋友很难找到，也很难改变。
This series of bit is suitable for drilling medium hard to hard formations with high compressive strength and medium abrasiveness.───适合在中硬至硬的高抗压强、中等研磨性的地层中使用。
Down-to-earth people work hard, to hard, obedience to a superior organization of work.───为人扎实肯干、能吃苦耐劳，服从上级安排工作。
Water condition: Medium hard to hard water.