The correct option is
A Are shown
NOTE: When the doer is the object of the sentence, we can say that the sentence is in the passive voice. Here, 'British television' does the act, and hence the sentence is in the passive voice.
As the given sentence is a general fact, we will use the simple present tense here. The programmes can be 'shown' on the British Television and not 'seen'
We use 'is/am/are' with the verb in the participle form to form the sentence in the simple present tense in the passive voice.
Option A - 'Are seeing' can be used in the active voice to form the sentence in the present continuous tense. Thus option A is incorrect.
Option C - 'Were seen' can be used in the passive voice to form a sentence in the simple past tense. As the given sentence is a general statement, we will use the simple present and not the simple past tense. Also, the programmes can be 'shown' and not 'seen'. Thus option C is incorrect.
Option D - 'Were showed' can't be used as it is grammatically incorrect to use the past form of the verb in the passive voice. Hence, option D is incorrect.
Option B - 'Are shown' can be used in the passive voice to form the sentence in the simple present tense. As 'programmes' is the plural subject, we can use 'are' here, and 'shown' is the past participle form of the verb. Hence, option B is the correct answer.
'Many American programmes are shown on British television.'