Spanish language Q&A Forum

El profesor llevaba hablando con el estudiante diez minutos cuando entramos en la habitación.

El profesor había estado hablando con el estudiante diez minutos cuando entramos en la habitación

Is there a general rule in Spanish about when the definite article must be used and when it can be omitted? Eg why do azúcar, sodio, carbohidratos and lácteos need the definite article but not pescado, marisco, granos and huevos? 

I am a bit frustrated with this lesson.  I guess my question is this: with my limited (A1) knowledge of Spanish, how am I supposed to know "that sometimes the feminine and masculine forms are the same" when repeatedly the test gives adjectives I do not (yet) know in Spanish?  

For example, placid.  I do not KNOW how to say placid in Spanish, thus how can I know if I should use the feminine adjective form or simply add mente?  The assumption of adjective knowledge doesn't work unless, as is sometimes done in the test, you GIVE the adjective form in the test question; example: Los coches son rápidos: van rápidamente.   In this example test question it is easy to understand rápidos (masculine form) will change to the feminine because I can SEE rápidos!  The frustrates me to get wrong when it seems to be testing me more on knowing a large range of adjectives in Spanish more than the specific assignment of adding the "ly" form! I don't see my scores getting better based on the lesson given.

In question #9: No ________ ni una cosa ni la otra, me da igual. 

(HINT: Conjugate "preferir" in El Presente)

Can you say,  ninguno de ellos instead?

Should the test questions note that the answer should be for Spain vs Central/South America? 

I don’t really understand how you can tell when not to translate verbatim? Is there a reason “ Now I cannot stop thinking about her” cannot be translated as “Ahora no puedo dejar de pensar en ella “. I am not seeing why it is translated as “ahora no dejo de pensar en ella”. Why wouldn’t the translation for that just simply be “now I don’t stop thinking about her”. Please help me understand why this is incorrect. These examples are the only reason I am doing poorly. Thank you. 

As stated by one example, "Yo conocí a Susana hace 6 meses."

However, as stated by another, "Hablé con Clara hace 2 horas." 

Why didn't the second example utilize "a"

Is it because "con" had already been used?