Which verb agrees in number with its subject? The new fluorescent light bulb ... to last more than 12 months.

a. Is built

b. Was built

c. Are built

d. Built

It cannot be c. since there is only one light bulb, not multiple.

It cannot be d. because there is no verb such as is or was

You could therefore either have the answer as a. or b. depending on if it is in the present or past tense.

However if I had to choose between the two I would rather go with a. 'is built'