Is there a rule on yesterday vs last night?

[Bigmo]

English Grammar Tests, Elementary Level

ESL/EFL Test #96 "prepositions of time: for, ago, since, on, at", question 8

His pet anaconda died five months ......... and he still misses it.

(a) for
(b) since
(c) ago
(d) on

English Grammar Tests, Elementary Level

ESL/EFL Test #96 "prepositions of time: for, ago, since, on, at", answer 8

His pet anaconda died five months ago and he still misses it.

Correct answer: (c) ago
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Is there a rule on yesterday vs last night - why not yesterday night?

Bigmo

[Mister Micawber]

.
'Yesterday night' is simply not idiomatic English-- but you can say it and be understood. Natives sometimes do when they are not thinking. We used to have 'yesternight', but it is now dead.
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Native English teacher at Mister Micawber's