This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Rickettsiae -a) Multiply only within living cellb) Produce typhus fever of epidemic type onlyc) Transmitted by athropod vectorsd) Respond to tetracycline therapy 
Select and explain. 
A. abc, B. ad, C. bc, D. acd
D: acd
Answer: D: acd 
Explanation: None