How to use prepositions of time?

[Ra Ny]

English Language Tests, Intermediate level

ESL/EFL Test #203 "Prepositions of Time and Date (1)", question 7

I called in to make an appointment and I can see the doctor ......... 3 pm. Can you come with me?

(a) (none)
(b) on
(c) at

English Language Tests, Intermediate level

ESL/EFL Test #203 "Prepositions of Time and Date (1)", answer 7

I called in to make an appointment and I can see the doctor at 3 pm. Can you come with me?

Correct answer: (c) at
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please explain this question

[Mister Micawber]

We are testing the use of the prepositions with time units. The rule is:

'At' a time ('at 3:00', 'at noon')
'On' a day ('on Tuesday', 'on August 26th')
'In' a month, year, etc. ('in August', 'in 2009')

Also remember these phrases: 'in the morning', 'in the afternoon', 'in the evening', 'at night'.
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Native English teacher at Mister Micawber's