The last question best uses a verb that agrees with its subject.
In the first sentence, the verb "needs" implies that the subject is singular. However, the subject(bricks) is plural. The correct verb would be: NEED
The second sentence actually had the opposite problem as the first. The subject (radio) is singular, but the verb "are" implies that it is plural. The correct verb would be: IS
The third sentence follows the same mistake as the second. The subject is singular (conductor), but the verb "are" implies that is plural. The correct verb would be: IS.
The last sentence is correct because the verb "are" implies that the subject is plural, and indeed it is! Buses is the plural form of bus.