Final answer:
The word manageable, formed by adding the suffix -able to the verb manage, means 'capable of being controlled'. It is an adjective describing something that can be effectively controlled or handled.
Step-by-step explanation:
The meaning of the word manageable is 'capable of being controlled'. When the suffix -able is added to the verb manage, which means 'to control', it forms an adjective that describes something that can be controlled or handled effectively. Therefore, the correct answer to what manageable means is option a, capable of being controlled. Options b, c, and d do not reflect the correct meaning of the adjective manageable.