The outer SQL query requires a green product:
$p.\mathrm{color}=\mathrm{'green'}$.
It outputs only the product name:
$p.\mathrm{name}=t.\mathrm{name}$.
The $\text{NOT EXISTS}$ clause says there must not exist another product $q$ such that:
$q.\mathrm{brand}=p.\mathrm{brand}$
and
$q.\mathrm{price}>100$.
Therefore the correct condition is
$\neg\exists q\in \mathrm{Product}(q.\mathrm{brand}=p.\mathrm{brand}\land q.\mathrm{price}>100)$.
Putting everything together gives C.
A reverses the $\text{NOT EXISTS}$ meaning.
B rejects the product if any expensive product exists anywhere, rather than an expensive product of the same brand.
D simply returns every green product tuple.
Hence,
Answer : C
