Use an only if the h is silent: an hour, an heir, an honourable man, an honest woman;
Use a when you pronounce the h: a hero, a hotel, a historian
(Writing tip: don’t change a direct quote if the speaker says, for example, “an historic”)
BEHIND SCHEDULE or FALL BEHIND SCHEDULE is a useful term when talking about delays or lateness, especially in a work context:
LET is used in many expressions and also forms many phrasal verbs. Below are some common uses: