Spanish language Q&A Forum

Can you say something like,  

De todos mis amigos, la mas guapa es Esmeralda. 

Of all my friends, the best-looking is Esmeralda. 

I held my breath several times!

Kwizbot           ¡Aguanté la respiración varias veces! 
You                  ¡Aguantaba la respiración muchas veces!

To me this seems this would be  ongoing : that he held his breath while things were happening….

Could the imperfect be used as well in this case? 

Thank you, Nicole

'If Cristina had married him'  -  why is 'se hubiera casada' marked wrong?

Didn't we learn in another lesson that we could substitute "que" for "porque"? Does that mean "debido a que" and "que" are also interchangeable via the transitive property? I feel like either I am misremembering or there are some nuances I'm not picking up on. 

Why is the (se) in parentheses in the title of the lesson? Every example is reflexive. Would one ever use a non-reflexive quedar in this context? (If not, it seems like the parentheses aren't needed, no?)