The correct answer is A.
Subjects and verbs must agree with one another in numbers ( singular or plural).
If the subject of a sentence is singular, the verb must also be singular. An example: My dog is sick. The subject of the sentence, 'my dog', is a singular noun and the verb 'to be' must therefore be in the 3rd person singular.
In the sentence My dogs are sick, the subject 'my dog' is plural ( there are many of the dogs, not only one ), so the verb to be must be in the 3rd person plural.
The subject Two prizes is plural ( two, more than one), so the verb here must also be in the plural form of the verb 'to be' which is are.