(1)① Stainless steel is not easy to rust and is often made into tableware, medical instruments or other instruments; (2) Helium has low density and stable chemical properties, and can be used for inflatable balls; (3) Gasoline is a mixture of various organic substances, which can dissolve various oils; ④ Liquid nitrogen is easy to vaporize and absorb heat, so cryosurgery can be used.
So the answer is: 1c2b3d4a.