Prepositions in-on

We use preposition in:

-When an object is inside of something.-For years, months, centuries and long periods.

Examples: -The keys are in the desk.-We finish the high school in 2017.-They celebrate their anniversary in May.-Argentina will progress in the next century.-The mankind will travel to Jupiter in the future.

Prepositions in-on

We use preposition on:

-To express a surface of something.-Days and dates.

Examples: -The ball is on the table.-Her birthday is on July the 5th.-We see us on Tuesday.- His birthday is on New Year’s Eve.