The document discusses different English grammar topics including the present perfect tense vs. simple past tense, past modals, and prefixes and suffixes. The present perfect tense is used for actions that occurred at an unspecified time in the past and continue to the present, while the simple past tense expresses actions that started and finished entirely in the past. Past modals like must, could, and might are used to speculate or make guesses about past situations based on evidence, with must having a 90% likelihood, could at 50%, and might at 30%. Prefixes are added to the beginning of words to change their meaning, while suffixes are added to the end. Examples of each are provided.

1. Unit 1
Present Perfect vs Simple past
Present Perfect Simple past
Structure has/have+verb in participle
• use present perfect tense to have
about events that occurred a non
specific time in the past and
continue to present.
• it is also used ″since″ and ″yet ″to
establish the time.
Explame
• I have already reat it
• She has not bought the hot
dog yet
Structure S+Verb past+c
• it is used to express actions
that started and ended in the
past.
• is used in expressions like Last
week, yesterday, that day,
when
Example
• You worked very hard last
week
• She lived in Japan last year

2. Unit 2
Past Modals
Use Past Modals to speculate,
deduce, or make guesses
about past situations based
on evidence.
Must -------- 90%
Could -------- 50%
Might -------- 30%
Example
• You could make your bed so room doesn't
looks such like a mess
• I would go to work, but I feel so lazy bad
• It Might be the best leave it tomorrow

3. Unit 3
Prefixes and Suffixes
Prefixes and suffixes are sets of letters that are added to the
beginning or end of another word
Prefixes
The prefixes are added to
the beginning of an existing
word to create a new word
with a different meaning
Example
wrap → unwrap
Suffixes
Suffixes are added at the end
of a word
Example
enjoy → enjoyable