"Shall" because for a prediction without evidence we use future simple, for predictions with evidence - "going to". "Shall" and not "will" is used for a stylistic effect, as "shall" is also a modal verb it's used here to emphasise the certainty, but the rule for predictions is still the same. Here you can scroll a bit down and see such usage: https://www.thefreedictionary.com/shall

I agree with you. The exercise is wrong and it has no key - it was written/edited by someone who doesn't understand how to use 'shall' properly. As Chris and Chris have said, 'will' or 'going to' are possibilities. 'Shall' makes no sense here. I'm a British English speaker, I do know how to use 'shall' properly, and I can assure you that this is NOT a correct use of 'shall' in any form of modern English. Believe what Mr Murphy says! Feel free to ask if you'd like me to explain why 'shall' is wrong.

Shall is correct, out of all the possible answers posed "Shall" makes the most sense. Other people here are stating that they think the answer should be "are going to" but that is not listed at all. The Key says that "Shall" is the correct answer so it's impossible that it's a typo because if it was a typo, then "are going to" would be mentioned in the Key as correct. "Shall" is the only correct answer posed here because there is no "are going to" and it's not a typo. I suspect that "are going" is meant to mislead. EDIT: It's used quite often. Examples are... 1) expressing a strong assertion or intention. "they shall succeed", "you shall succeed" 2) "NOW this is the Law of the Jungle — as old and as true as the sky; And the Wolf that shall keep it may prosper, but the Wolf that shall break it must die."

I agree with Su. Ki. and Chris. My choice is also “are going to.” My North American viewpoint: - I predict that you shall marry ... Shall is rare and usually has a directive meaning in legal and business documents in North America (as Chris mentioned in his example “employees shall never leave work without notifying their superiors"). Here the combination of “I predict” and “you shall” is nonsensical to a North American. If it occurred in a British movie, it would be accepted as a British-ism. - I predict that you will marry ... A natural-sounding prediction about the future, but not one of the available answers. - I predict that you are going to marry ... A natural-sounding prediction about the future. - I predict that you should marry ... Should conveys soft obligation or strong advice in North America (as in “Students should get extra sleep the night before an exam”). Here the combination of “I predict” and “you should” is nonsensical to a North American. If it occurred in a British movie, it would be accepted as a British-ism.

In American English, the situation is much simpler than in British English. Here, we never use "shall", unless we are attempting to sound intentionally old-fashioned, or unless we are writing formal regulations ("employees shall never leave work without notifying their superiors"). In America, we would use "will" or "are going to".