Spanish language Q&A Forum

In the test the question is "Coloca las plantas _____ sol." I understand that "al" is the correct answer as far as a contraction, but why do you use "a" in this instance? Why is it not "en el sol"?

I'm almost 2 years into learning Spanish and I get lost after hearing a couple of words if I close my eyes.  I watch shows and listen to Spanish podcast, and my ear for Spanish has not developed at all.  What could I possible do to change this?

Why 'comí' una lubina, then 'tomé' un trozo, but with the same english translation?

I've read the answers below, but there are still instances where I'm confused. For example, the test answers say that "Lo están llamando" is the correct translation of "They're calling him." However, I think I saw "They're writing him" translated as "Le están escribiendo." Both take the preposition "a" when the person being called or written is named, and both can use the preposition "to" in English. How is it possible to know that llamar takes a direct object, while escribir takes an indirect object? 

I was taught podrías means could when talking about the future and podía means could when talking about the past. Is this wrong?

can you explain why, even though we're talking about a female, we would say "trabajas duro"? Gracias!