PRES.S always, usually, generally, often, frequently, sometimes, seldom, never.
PRES.C now, right now, at the moment, today, this year, these days, tonight, tomorrow.Estoy comiendo.
PAST.S yesterday, last week, two days ago, in 2004, when, them comí. PAST.C last night, at 3.00h, when, whilw, as. Estaba comiendo.
PRE PERF S.Never, ever,yet,alrready, just for, since. He comido
PRE PERF C. For a month, since, all night.He estado comiendo.
PAST PERF S alrready by the time before untl never just when as soon as ha comido
PAST PERF C for hours since all night when until habia estado comiendo