The correct option is C are not allowed
A sentence in passive voice focuses on the person or thing that receives an action rather than the person/thing that performs the action.
For example, 'My room was cleaned by me.'
The basic structure of passive voice is:
the appropriate form of the verb 'to be' + past participle
Option B: The given sentence states a fact (in the negative), hence it's in simple present tense. So, the simple present form of 'to be', 'are' is used. (The simple present tense states a general fact or a usual habit.)
'Are not allowed' is the appropriate structure, formed by the simple present tense verb 'are' + the negative adverb (not) + past participle (allowed). Hence option B is correct.
Option A: 'Allow' is the base form of the verb whereas the past tense form (allowed) is used in the passive voice. Hence A is incorrect
Options C and D: 'Does' and 'do' are verbs in the active form (does is a form of 'do' in the present tense). The word 'do' itself means 'to perform an action'. These words are not used in the passive voice.
Hence options C and D are incorrect.