What is the rule in this case?

[Gonza]

English Grammar Tests, Elementary Level

ESL/EFL Test #91 "Using Prepositions", question 4

All of Chris' teachers agree that he is very good ......... math.

(a) with
(b) for
(c) at
(d) on

English Grammar Tests, Elementary Level

ESL/EFL Test #91 "Using Prepositions", answer 4

All of Chris' teachers agree that he is very good at math.

Correct answer: (c) at

Your answer was: incorrect
All of Chris' teachers agree that he is very good on math.
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What is the rule in this case?

Gonza

[Alan]

Hi,

I think it's impossible to limit and define the use of a particular preposition. All I can say is that on has the sense of on the topic of/on the subject of as in: There is a film tonight on tv on the war. At generally is less direct so we say: good at/clever at/bad at/.

I have done a piece on prepositions and their use for this site, which you may find useful

ESL Lesson: Prepositions
http://www.english-test.net/lessons/4/index.html

Alan
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English as a Second Language
You can read my ESL story Indirect Speech