Correct Option: C

backslide (Verb) : drop to a lower level in one’s morals or behaviour
regress (Verb) : to return to an earlier or less advanced form or way of behaving
deteriorate (Verb) : to become worse (bad to worse)
degenerate (Verb) : deteriorate
lapse (Verb) : to be no longer valid because the period of time that it lasts has come to an end