Any.
The hide of a cow. There is no "kind" of cow skin, just any old cow skin that has been tanned into leather is used.
without them we wouldn't have any kind of beef, no milk, or leather.
Leather can be made out of just about any kind of animal skin. Leather wallets are no exception though on example of a good quality leather wallet is made out of buffalo calf hides.
Mussels and chips with mayonnaise. Its not disgusting/ weird its just different.
microwave
Yes.
It depends on what kind of vegan you are. There's no law that says that if you are this kind of vegan, you cannot wear leather, or anything like that. If you're the vegan and you are uncomfortable with wearing leather, trust your heart and feelings. Wear substitutes for leather instead.
Cows are the primary sources of leather, but they can also be made out of snake and any other animal that has the skin the same texture and durability as cows do.
The best way to get the rust off of leather seats is to not let it get there in the first place but if that is not avoidable then you can use any kind of highly rated leather cleaning products such as armor all.
Any element can melt.
You can melt ANY kind of chocolate. White chocolate, Milk chocolate, dark chocolate, ANY kind at all. that can be true but its better to melt cooking chocolate it is more smooth and creamy!