not the brightest star in the sky

[Baubau]

English Language Tests, Intermediate level

ESL/EFL Test #436 "English Slang Idioms (175)", question 6

"I like Matt but I don't want to work with him on a group project. He is a hard worker but he's not the ......... star in the sky," Luke told Joe.

(a) one
(b) dimmest
(c) bluest
(d) brightest

English Language Tests, Intermediate level

ESL/EFL Test #436 "English Slang Idioms (175)", answer 6

"I like Matt but I don't want to work with him on a group project. He is a hard worker but he's not the brightest star in the sky," Luke told Joe.

Correct answer: (d) brightest

Your answer was: correct
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Hello,

What does "not the brightest star in the sky" refer to? Intelligence, skill, personality...?

Thanks in advance.

[Kitosdad]

He is not very intelligent.
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Keep it simple ... Keep it interesting.