What Was the Roman Attitude Toward the Manumission of Slaves

What was the Roman attitude toward the manumission of slaves?

A) Manumission of slaves was so common that laws were passed limiting the practice.
B) Slaves were only manumitted under exceptional circumstances, when state authorities agreed that the slaves deserved special treatment.
C) Slaves were manumitted by law at age 55 if they had been faithful workers.
D) The manumission of slaves was forbidden by law.