in today’s lesson we learned that en is used to replaced object s in a sentence which follow de+a partitive article (any, some); de+ an indefinite article (de, du des) ; a measurement of quantity : beaucoup de , un peu de

if you paid attention you would have noticed that the common thread was a form of de; either de la, du (de le) or des or un, une (indefinite article whose plural is des )