In general, the present perfect (me ha llamado) implies something ongoing or unresolved: "The owner has called me to his office." The preterite (me llamó) implies a completed or self-contained activity: "The owner called me and left a message."
But there is some overlap: in casual conversation, "I ate" (Yo comí) means almost the same thing as "I have eaten" (Yo he comido).
Hope this helps.
In Spanish from Spain, there generally use the present perfect for events that occurred recently ... that same day or that morning or afternoon. Spanish from Latin America is much more likely to use the preterite in exactly the same situation.
This is particularly true in Spain if the sentence includes "esta" as in esta mañana, or even "esta semana.
If something happened yesterday, in more cases the preterite is used no matter what version of Spanish is spoken.
Don't make more work for the devs just because a different language does something. Research the causes in Spanish. If there's a good reason for it, then report it.
In this case, it is not simply interchangeable, and shouldn't be reported as such. Past perfect and similar grammar are used to convey when things happened on a timeline in a relatively small amount of words.
Think of this exercise's sentence as happening in the middle of a conversation, where something happened, and we respond with something that happened - the owner called - earlier. We could say "The owner called me earlier, before that other thing you were talking about happened," but it is much simpler (once we understand the grammar) to just say "The owner has called me."
i don't understand why the sentence has to have "has called" when the has is implied in English.... The owner called me. = The owner Has called me. the comments already say the auxiliary verb is needed ... maybe in Spanish, but not in English ...
It is those differences in language that are important to learn .... not speaking funny in English to get the answer right.
The English sentence may not be used often, but it is important to understand the correct grammar translation. There is a difference between the sentences you used as examples. http://grammar.about.com/od/basicsentencegrammar/a/prperfectense.htm
This sentence is present perfect. Even though the auxiliary verb is in a present tense, perfect sentences generally refer to something that happened before the reference time, while the action still has an impact on the reference time.
Example: "Have you eaten yet?" - Asking whether you ate recently and if the satisified feeling of a full belly still applies to you.
"The owner had called me" is past perfect, referring to an action that happened before an action in the past. Example: "I wanted to order pizza like every Tuesday, but then I remembered that the place's owner had called me the day before to let me know that their oven is broken."
I'm not sure about the Spanish, but in French, which is a language from the same group, the equivalent form "a appelé" is called passé composé and may refer to either an action from the passed period, in which case it is equivalent to the Present Simple ("called"), or to an action that has taken place before the moment of speaking no matter when, in which case it is equivalent to the Present Perfect tense ("has called"). So, if that is also the case with Spanish, both translations are possible; the choice depends on the context.