81.Superphosphate fertilizer is perpared by the reaction between

82.Consider the following statements about antigens : 1. They induce the formation of antibodies. 2. They provide immunity. 3. They are formed only within the body.Of these statements, the correct ones are

83.The major ingredient of leather is

84.In a refrigerator, cooling is produced by

85.Ball bearings are used to reduce friction by