Read the following article and answer the question by choosing from the options.

I got randomly selected at work to test my " signature " basically like mystery shopper but over the phone . Anyway I got 3/10 which is pretty bad . I even got to listen to my conversation which in my defense was at the end of a 10 hour straight shift of answering phones . I sounded half asleep I never realised just how slack and full of slang the Aussie accent is .

What may be the reason why they were so tired ?
OPT:
A). They did n't sleep the night before .;
B). They were up late studying .;
C). None of the above choices .;
D). They are not used to working such a long day .;...A:
D).