Possible invalid question on CAT

[Gui]

I believe that this question (bellow) of Manhattan CAT maybe wrong/ invalid. Can you please check it?

Which of the following expressions CANNOT have a negative value?

a) |a + b| – |a – b|
b) |a + b| – |a|
c) |2a + b| – |a + b|
d) aˆ2 + bˆ2 – 2|ab|
e) |aˆ3 + bˆ3| – a – b

The "official" answer is D, but if 'a' and 'b' are 0, then the expression is equal to -2, correct? So, there is NO answer.

Many tks!

[Sage Pearce-Higgins]

Well done for checking, however, if a = b = 0, then ab = 0, so |ab| = 0, so 2|ab| = 0, and the expression would equal 0, which is not negative.