Spanish language Q&A Forum

Okay. I'm really confused. How did I get half of these questions wrong. I know Spanish. But yet, I got some of these questions wrong.

In this question I answered "éramos" instead of "fuimos" since the text referred to "used to be."  Why was that wrong? I get that  the "completed action in the past" hint confused the situation. Shouldn't the question be clarified, or am I missing something here? 
Nosotros ________ muy buenos estudiantes.We used to be very good students.(HINT: Refers to a completed action in the past.)

From the lesson:

"Note that while "fue" is generally translated into "was" in English, "era" can be translated into "was", "used to be" and "would be"."

I am still confused when to use and when to omit the definite article.  I end up guessing, which is sometimes right and often wrong.  Example 1: "En lo que se refiere a incendios forestales." We're talking about forest fires in general and there is no definite article "los".  Example 2: "Es importante que no nos olvidemos del cambio climatico."  The English statement is that we must not forget about climate change in general.  This time there is the definite article "el" or "del".  Is there a rule or guideline that might clear this up for me?  Thanks.

“but another one with that voice”. 

porque dice eso no es correcto en el primer paso

why did it say it was wrong in the first part

How would you say "her/his leg hurts"? Would it be "Ella/El duele la pierna”?

I put "Acabo de comprar un apartamento "  and that was not shown as a possible answer for "I just bought an apartment " but I believe it is correct.

For the example:

De no llegar a tiempo perderíamos el vuelo.
If we didn't arrive on time we'd miss the flight.
I can only see four translations:(1) If we don't arrive on time we'll miss the flight. (or "we could miss")(2) If we hadn't arrived on time we would/could have missed the flight.
Could you please double-check your English translation?  Thanks.