TASK DEFINITION: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
PROBLEM: Possible Duplicate: 'Did it close' vs 'Has it closed'? As a English non-native speaker it is difficult for me to understand when I must use present perfect or past simple because in my official language there isn't the present perfect tense. I know that present perfect is related to something that happened in the past but its result is important now. But for instance: The message has been sent. The message was sent. Please help me point me out any examples/contexts where I should use 1. instead of 2.

SOLUTION: 1 means that the action happened just now. You would typically see it in your e-mail program just after you send an e-mail. Your program might give you this message to let you know that the message you just sent has indeed been sent. 2 refers to something that happened at some time in the past. It could have been an hour ago, a day ago, or even a century ago! But it wasn't just now.

PROBLEM: I'm describing what an opiate addict looks like before recovery. Instead of saying 'he looked like a vampire,' I'd like to say something like 'he looked [vampiric].' I actually just found out vampiric was a word, but I want something that sounds better (more colloquial/natural, I suppose) and covers a variety of traits (pale, emaciated, sickly, etc). Why I don't just use 'vampiric': As @chepner commented: I think the idea is to find a word that isn't so 'circular', and doesn't refer explicitly to vampires or require knowledge of vampires in context. If someone were to ask 'What does a vampire look like?', then 'It looks vampiric/vampirish' wouldn't be terribly helpful. I don't want to explicitly refer to drug addicts as vampires. I just want to capture those traits in the best way.

SOLUTION: I'd suggest cadaverous. It incorporates many facets of what I believe you're trying to convey: a corpse-like appearance, including pallid and underweight. From Merriam-Webster.com: 1a : of or relating to a corpse b : suggestive of corpses or tombs 2a : PALLID, LIVID b : GAUNT, EMACIATED grossly underweight

PROBLEM: E.g. is short for exempli gratia, and is in common use to introduce an example within a sentence. Submit a sample of academic writing, e.g., a dissertation chapter. However, some authors use ex. or ex: (short for 'example') for the same purpose, and this form is listed in some authorities like the Wiktionary. Submit a sample of academic writing, ex: a dissertation chapter. I know they both roughly mean 'example', but which one should I use, and when? Are there connotations associated with one or the other? This question has been asked elsewhere, and this very answer comes up when you ask Google about the difference. It would be good to get an EL&U answer for it.

SOLUTION:
E.g. is short for exempli gratia and stands for 'for example'. Ex., if used to mean the same, is incorrect. Mostly ex. is used as short for exercise and not 'for example'.