Assimilation

Some English consonant sounds, change into different phonemes when followed by certain other sounds. Here are some examples

/ t / changes to / p / before / m / / b / or / p /

Great Britain
pot plant
put back

/ d / changes to / b / before / m / / b / or / p /

blood pressure bad boy / n / changes to / m / before / m / / b / or / p / down payment open book / t / changes to / k / before / k / or /g/ credit card fat girl / d / changes to / g / before / k / or / g bad girl hard cash / n / changes to /ŋ/ before / k / or / g open court Golden Gate