Why is the sutta called the 'Karaniya Metta Sutta'?

• aBecause it was first recited in a place called Karaniya
• bBecause it gives a guideline for those wishing Nibbana to practise mettabhavana as their duty
• cBecause it was composed by a monk named Karaniya
• dBecause it protects from famine