Identify the mismatched pair.
`{:(,"Hard magnet","Alnico"),(,"Soft magnet","Soft iron"),(,"Bar magnet","Equivalent solenoid"),(,"Electromagnet","Loud speaker"):}`
A. `{:(,"Hard magnet","Alnico"):}`
B. `{:(,"Soft magnet","Soft iron"):}`
C. `{:(,"Bar magnet","Equivalent solenoid"):}`
D. `{:(,"Electromagnet","Loud speaker"):}`
