Spanish language Q&A Forum

I'm having trouble understanding this answer in a study plan test.  Could you please explain.

Ella estaba lavándose el pelo cuando él llegó.
She was washing her hair when he arrived.

When it is combined with another action that interrupts the ongoing action at that time. The interrupting action is generally in the simple past (see the last example where the ongoing action "She was washing her hair" was interrupted by another sudden action "he arrived”.

 Te ________ hasta que me aburrí y me fui.  
I was waiting for you until I got bored and left.

era esperando
estaba esperando-----my answer
estuve esperando------correct Kwiziq answer
fui esperando

 To me, it seems that the waiting was interrupted by "got bored and left."

There was a question in one of the quizzes I took and it led me to this grammar topic (questions with qué):

Which flowers do you prefer?  

¿ _____ flores prefieres ? 

I put cuales in the blank, but was marked wrong, it said the answer was qué. 

I went to the lesson on cual/cuales (interrogative pronouns) and there was a sample sentence referring to flowers, using cuales prefieres.  

In the English translation to the quiz it uses which and I assumed that a select few flowers were being referred to, thus the answer should be cuales. It is a bit ambiguous. 

First of all, how to decide when to use despertar and when despertarse?

Second question, why can't we use levantarse in place of despertarse?

Happy birthday to you.  Why is ti used and not te?   I can’t find a lesson on the use of ti instead of te. For instance para ti

In the introduction to this lesson, you say the meaning is similar to using "haber plus infinitive". I think you mean haber plus past participle i.e. the perfect tense

"Hurry, Run!"  Can I interpret "Hurry" as Command, too? If so, none of the options is appropriate. 

If gustar is followed by a verb, you always use gusta, right? Example: Me gusta nadar con los delfines. VS Me gustan los delfines. 

Am I understanding that correctly?