Translate the following paragraphs into Chinese. The primary drawbacks to the magnetic and acoustic approaches are the need for external guidance—which is cumbersome—and the fact that magnetic fields and ultrasound waves can penetrate only so far into the body. Developing autonomous “micro motors” for the delivery of therapeutic cargo could surmount those problems. Such micro motors would rely on chemical reactions for propulsion, but toxicity is an issue. For example, oxidizing glucose, a sugar molecule found in the blood, would generate hydrogen peroxide, which could be used as a fuel. But researchers already know that this particular approach would not work in the long run. Hydrogen peroxide corrodes living tissue, and glucose in the body would not produce enough hydrogen peroxide to adequately power micro motors. More promising are efforts to use other naturally occurring substances, such as stomach acid (for applications in the stomach) or water (which is abundant in blood and tissues), as power sources. Accurate navigation by these self-propelling devices may be an even greater hurdle, however. Just because nanoparticles can move anywhere does not mean that they will necessarily travel exactly where researchers want them to go. Autonomous steering is not yet an option, but a work-around would be to make sure that nanomedicines become active only when they find themselves in the right environment.