Correct - we say it when we are talking about a dead person

For b) to be correct, it should read: 'That letter must HAVE arrived'

It's difficult to answer this question because I don't know what the test is, or what its purpose is. Are they only testing your language? Or are they testing you knowledge in other area too? In general, most spoken English tests are looking for these things: 1. How well you answer the question. 2. Vocabulary and grammar - both accuracy and range (showing that you can use many different words and sentence structures). 3. Pronunciation. Remember, you don't need to be perfect!

Yes, in this case 'would' is simply the past tense of 'will'. In the present: 'The officer will not say...' = does not want to say So in the past 'will' becomes 'would'

There could be different ways of understanding these terms, depending on who is using them and the situation. But I think what you want is: Time = the time an event occurs in the real world: past, present or future. Tense = the form of the verb which indicates time. In English time and tense don't always match. For example we can use present continuous (I'm working) to refer to present or future time, and past tense to refer to past time or imaginary present/future time ('If I was rich..')

There is a rule. In this type of sentence there are two clauses (parts) - the main clause (which tells you what will happen) and the time clause (which tells you WHEN it will happen, usually starting with 'when/after/before'). For the main clause we use the future tense as normal (will/going to, etc). For the time clause we use a PRESENT tense, even though the event happens in the future. A present tense means either present simple or present perfect, depending on whether the action will have finished. 'When we VISIT Paris, we'll see the Eiffel Tower' 'When we HAVE VISITED Paris, we'll go to London' (='AFTER we VISIT Paris...')

All of these mean more or less the same thing and are interchangeable. The difference is more in the culture and context. For example, (in the UK at least) a comedy night has a compere, while a formal dinner would have a host. MC sounds fine in your context above. Probably the most neutral term, if you're not sure which to use, is 'host'.

They're the same.