Answer:
The correct answer is b. dawn and dusk.
This is because Gila Monsters are crepuscular in nature i.e. they are the organisms which are highly active during twilight (the periods of dawn and dusk).
In contrast, diurnal organisms are those which are active during the day time for example dog, squirrel, gorilla etc. and nocturnal organisms are those which are active during the periods of darkness such as owl, bat etc.
Similarly, matutinal is the term used for the organisms which are active before sunrise and vespertine is a term used for organism which are active only post sunset.