Final answer:
The correct answer is 'are going'.
Step-by-step explanation:
The correct answer is B) are going.
In this sentence, Marry and her husband are the subject and they are both going on a journey. Since the subject is plural, we need to use the plural form of the verb 'to go', which is 'are going'. So the correct sentence is: 'Marry and her husband are going on a journey tomorrow.'