Spanish language Q&A Forum

I am confused after getting an answer wrong in a test and then reviewing the subsequent lesson.   

In a recent test, this sentence was given to complete.   "No me gusto nada hacer ejercicio _____________."  My answer was "después de comer," when in fact the answer was "después de comiendo."   

I went back to review the lesson and the lesson states that after the preposition "de" comes the infinitive form of the verb to say the "ing" form of the verb.    Now I am confused as to why my answer of "después de comer" is not correct.   When do you use the infinitive?  and when do you use the present participle (i.e. ending "ando" or "iendo") after the preposition de?

If cuál  means "which" and the question is "which" flowers NOT "what" flowers when would cuál ever be used?  Tengo dos flores cuál  prefieres?

The speakers are having a phone conversation.There, where you live, is it cold? : ___, donde tú vives ¿hace mucho frío?

Why is alli not possible in this question? Considering that they are on the phone, they might feel quite far apart from each other.

Just a note that, by and large, a literal translation mostly works here as well, although the construction sounds a little English (vs. American) to me. To wit: "They will have gone to bed upon arriving at the hotel because the trip was very long" is perhaps an unusual phrasing in modern conversational (American) English, but certainly not an unintelligible one, and I think it carries the same meaning. 

What are the equivalents for can't & must not for logical conclusions in Spanish? That is, how can I express the difference in meanings given in the following examples?

(present)

The restaurant can't be open - the door is locked

The restaurant must not be any good - it is always empty

(Past)

He had left the office at 6:00 p.m. He can't /couldn't have been at home at 6:05 p.m

She was not answering the doorbell. She must not have been at home then.

Regards,

Alexander

When is "de la mañana" used?

In the question:

They will be very cold when they go to Scotland next December.

It seems to me that this is a quite certain plan, like one of the examples here: ‘ Cuando voy de vacaciones a Tenerife me hospedo en el hotel Olimpia.’

So I thought the answer should be in the indicative:

Tendrán mucho frío cuando irán a Escocia el próximo diciembre.

But the correct answer was in the subjunctive:

Tendrán mucho frío cuando vayan a Escocia el próximo diciembre.

Why is that? Is it a mistake?

This device is often used in story telling and especially in jokes. E.g. "A man goes into a pub and asks the barman ......" It adds a freshness and immediacy to the narrative.