The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

The OBSERVATION period
is almost over,
Westworld Season 2, Episode 4

Tell my friend you need to keep me
under OBSERVATION for an hour.
The Big Bang Theory Season 1, Episode 16

As a scientist, I reach conclusions
based on OBSERVATION and experimentation.
The Big Bang Theory Season 1, Episode 10

OK? For some OBSERVATION.
Westworld Season 2, Episode 4

Are you familiar
with Darwin's OBSERVATION...
The Big Bang Theory Season 4, Episode 18