In the following examples, mechanical energy is converted into internal energy by (). A. Power stroke of gasoline engine. B. The iron wire is repeatedly bent, and the temperature at the bend of the iron wire is increased. A, gasoline engine power stroke, internal energy can be converted into mechanical energy, so a is wrong;

B. Repeatedly bending the wire, the temperature at the bend of the wire rises, and the mechanical energy is converted into internal energy, so B is correct;

C, mobile phone talk time is too long, it will make electric energy heat up and convert it into internal energy, so C is wrong;

D. When the metal spoon is put into hot soup, its temperature rises, which increases the internal energy of the object through heat transfer, so D is wrong.

So choose B.