Помогите задать к тексту 2 специальных и 1 общий вопрос: When I choose a material for a bike frame, I have to think about the properties of the material. How elastic Ís it? If you bend or stretch it, will it go back to its original shape? If it does, it has high elasticity. How strong is it? There are two kinds of strength. The first is how much force you need to bend it to a point where it cant go back to its original shape. The second is the amount offorce you need to break it. Steel is the least expensive choice. Theres a wide range of standard gauge tubes available. Its strong and it has good elasticity but its heavy. Aluminium is lÍght and strong but it,s flexible. The more it bends, the quicker Ít breaks. So aluminium bike frames use large diameter tubes. That limits the amount of bending. Titanium has a great strength.to.weight ratÍo. It,s got good elasticity so when it bends it tends to return to its original shape. Its corrosion-resistant so you don,t need to paint it. But its expensive - fifteen times the price of steel! The professÍonals use carbon fibre. Its very light and its very strong. You can shape it any way you like. But carbon-fibre frames are hand-made so theyre very expensive

 What are two kinds of strength?