you should try to get a good night`s sleep

you should try to get a good night`s sleep
You should try to get a good night’s sleep ______ much work you have to do.
选项:
a、however
b、 no matter
c、 although
d、 whatever
为什么是A,however 不是一般都有加“,
我知道however=no matter how,我怎么感觉是C?翻译起来也挺顺的啊……“你应该尝试去有一个好的睡眠,总是有很多工作你不得不去做.