Passive Verb Formation

The passive forms of a verb are created by combining a form of the "to be verb" with the past participle of the main verb. Other helping verbs are also sometimes present: "The measure could have been killed in committee." The passive can be used, also, in various tenses. Let's take a look at the passive forms of "design."

Tense	Subject	Auxiliary		Past Participle
		Singular	Plural
Present	The car/cars	is	are	designed.
Present perfect	The car/cars	has been	have been	designed.
Past	The car/cars	was	were	designed.
Past perfect	The car/cars	had been	had been	designed.
Future	The car/cars	will be	will be	designed.
Future perfect	The car/cars	will have been	will have been	designed.
Present progressive	The car/cars	is being	are being	designed.
Past progressive	The car/cars	was being	were being	designed.

A sentence cast in the passive voice will not always include an agent of the action. For instance if a gorilla crushes a tin can, we could say "The tin can was crushed by the gorilla." But a perfectly good sentence would leave out the gorilla: "The tin can was crushed." Also, when an active sentence with an indirect object is recast in the passive, the indirect object can take on the role of subject in the passive sentence:

Active	Professor Villa gave Jorge an A.
Passive	An A was given to Jorge by Professor Villa.
Passive	Jorge was given an A.

Only transitive verbs (those that take objects) can be transformed into passive constructions. Furthermore, active sentences containing certain verbs cannot be transformed into passive structures. To have is the most important of these verbs. We can say "He has a new car," but we cannot say "A new car is had by him." We can say "Josefina lacked finesse," but we cannot say "Finesse was lacked." Here is a brief list of such verbs*:

resemble	look like	equal	agree with
mean	contain	hold	comprise
lack	suit	fit	become

Source:http://grammar.ccc.commnet.edu/grammar/passive.htm