**Core Concept**
The embryonic disc is the earliest stage of embryonic development, consisting of three primary germ layers: ectoderm, mesoderm, and endoderm. These layers give rise to all tissues and organs in the body.

**Why the Correct Answer is Right**
The correct answer represents the three primary germ layers of the embryonic disc. The ectoderm is the outermost layer, which gives rise to the central nervous system, skin, and other external organs. The mesoderm is the middle layer, which forms the muscles, bones, and connective tissues. The endoderm is the innermost layer, which develops into the lining of the digestive tract, respiratory system, and other internal organs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it only represents two of the three primary germ layers.
**Option B:** Similarly, this option also represents only two of the three primary germ layers.
**Option C:** This option is incorrect because it represents a different stage of embryonic development, such as the gastrula, which is formed after the embryonic disc.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the three primary germ layers are the foundation of all tissues and organs in the body, and understanding their development is crucial for grasping embryology and human anatomy.

**Correct Answer: C. The embryonic disc consists of three primary germ layers: ectoderm, mesoderm, and endoderm.**