Meaning of 'apple of your eye'

English Language Tests, Intermediate level

ESL/EFL Test #279 [color=blue]“English Slang Idioms (1)”, question 3

I spoil my grandson because he’s the apple of my .

(a) orchard
(b) heart
(c) yard
(d) eye

English Language Tests, Intermediate level

ESL/EFL Test #279 [color=blue]“English Slang Idioms (1)”, answer 3

I spoil my grandson because he’s the apple of my eye.

Correct answer: (d) eye

Your answer was: [color=red]incorrect
I spoil my grandson because he’s the apple of my heart.
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what does the expression:, he’s the apple of my eye’'mean?
thanks:)

If someone is the ‘apple of your eye’, they are appreciated, loved, or cherished above others.