This topic examines the principles of effective defense. The principle of effective defense is the embodiment and guarantee of the right of defense. In criminal proceedings, defense should be of substantial significance to protecting the rights of criminal suspects and defendants, not just in form, which is the basic requirement of effective defense principle. Specifically, the principle of effective defense should include the following aspects: (1) Criminal suspects and defendants, as parties to criminal proceedings, should enjoy full defense rights in the whole proceedings; (two) allow criminal suspects and defendants to hire qualified defenders who can effectively perform their defense duties to defend them. This kind of defense should also cover the whole process of criminal proceedings from investigation to trial and even execution: (3) The state should ensure that criminal suspects and defendants fully exercise their right to defense, and through the establishment of a legal aid system, ensure that criminal suspects and defendants can get the help of lawyers who meet the minimum standards and have substantial significance. The establishment of the principle of effective defense is the embodiment of the civilization and progress of human society in criminal proceedings. It embodies the concept of establishing the subject status of criminal suspects and defendants and protecting human rights. This is also helpful to strengthen defense as an important force affecting the litigation procedure and maintain the criminal litigation structure of equal confrontation and "simultaneous hearing" in court trial. Therefore, this question chooses AD.