My class starts at eleven o'clock.

I eat lunch at twelve o'clock.

He has been committing misdeeds for many years, but finally the time for repayment has come.

Greenwich Mean Time is the standard that determines the time of the world.

He likes to take a walk in the park at dusk.

Sandwich compounds are being studied in a branch of chemistry.

He always buys cheap things, so in the end, it becomes 'penny wise and pound foolish'.

Acidic oxides react with water to produce acids.

Aluminum is an amphoteric oxide, it reacts with both acids and bases.

Peroxides play an important role in chemical reactions.