The correct option is
E Keep up
“To hold up” means to remain strong or vigorous, it means to continue to stay so.
“Abide by” means to follow the rules meant to be abused by.
“Retain” means to continue to have.
“Support” means to bear the weight, also means to give assistance to.
“Side with” means to agree with someone
“Keep up” means to meet a commitment, or to do something regularly, continuously. Hence option E is the correct answer, it is the correct meaning of the given phrase.