U.2: have been improving over the years/ had been complaining.
can: poder / be able: poder / can´t: prohibición, no poder / could: past ability, polite request and suggestion / may: posibility / would: formal requesst, offer / must: obligation / have to: obligation / need to: obligation / needn't and dont have to: no tener que / musnt: prohibition / should: advice / shall: offer, suggestion.
U4. ESTILO INDIRECTO:
Eat: ate // ate: had eatem // will eat: would eat // are eating: were eating // were eating: had been eating // have eaten: had eaten // have been eating: " // had eaten: " / had been eating: " THE PREVIOUS/ THE FOLLOWING/
U.5. PASIVE: writes: are written / wrote: were written / will write : will be written / is written: are beeing writting / was written: were beeing written / has written: have been " / had written: Had been " / sould write: should be " / must have ": Must have been " / has to write: have to be " / is going to write: are going to be ". // IT IS SAID THAT/ IT IS KNOWN THAT/ ARE BELIVED TO/ IS CONSIDERED TO.