An experiment is set up to test whether a particular insect prefer a dark or a bright environment. A chamber with a gradient in light intensity from one end (dark) to the other (bright) has been made. The experimental hypothesis is:

“There will be a large difference between the number of insect in a dark side and the number in a bright side of the chamber.”
Which one could be the three confounding variables?

A - Varying humidity across the chamber
B - The orientation of the chamber
C - The age of the insects :no
D - The non-reflective material from which the chamber is made
E - The type of light source used
F - Varying temperature across the chamber

I was thinking A, E and F but there is something wrong even A,B and C is wrong
Any help would be appreciated. Thanks

I would agree definitely with A and F. Also E, if the light source did not cover the spectrum similar to sunlight.