Alexander technique is a therapy in complementary medicine for improving health by teaching people to move, sit and stand efficiently. It is designed to release unnecessary muscle tension in order to eliminate or reduce the severity of a wide range of disorders like back pain, asthma, repetitive strain, injury and stuttering. Training is carried out in one-to-one sessions under a qualified teacher. The technique was started by F Matthias Alexander in 1890 for his breathing problem and hoarseness.

We observe that among the given choices, Option C best captures the essence of the passage by highlighting: (i) the focus on posture and releasing muscle tension, (ii) the goal of addressing a number of disorders, and (iii) the role of a qualified teacher (mentioned in the text as "one to one sessions under a qualified teacher").

Contrarily, the remaining choices are either incomplete or misleading. For example, while Option A mentions the origin of the technique, it fails to capture the core purpose of the therapy or its application to a wide range of disorders. Option B also misses the focus on posture, muscle tension, etc. and its benefits for various disorders. We can eliminate Option D on similar grounds: though it lists some of the disorders the technique can address, it doesn't explain how the therapy works.