**Core Concept:** Ossification is the process by which cartilage is replaced by bone tissue. In humans, it occurs in two phases: primary ossification and secondary ossification. Primary ossification begins in the second month of pregnancy, while secondary ossification starts in the seventh month.

**Why the Correct Answer is Right:** The first centres of ossification are called the primary ossification centres, which appear in the second month of pregnancy. These centres are responsible for the formation of the long bones in the limbs and the skull. The primary ossification centres undergo a process called endochondral ossification, where cartilage is gradually replaced by bone tissue.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because ossification begins during the second month of pregnancy, which is after the correct answer (Option C).
B. This option is also incorrect because ossification begins during the second month of pregnancy, as mentioned earlier.
C. This option is the correct answer, as it states that ossification starts during the seventh month of pregnancy for the secondary ossification centres.
D. This option is incorrect because it refers to the development of teeth, which is a separate process called odontogenesis and occurs independently of ossification.

**Why the Correct Answer is Right:** The first centres of ossification, also known as the primary ossification centres, appear in the second month of pregnancy. These centres are responsible for the formation of long bones and the skull. The process of ossification involves the replacement of cartilage with bone tissue, a process called endochondral ossification.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because it refers to the development of teeth, which occurs independently of ossification in the dental lamina and is called odontogenesis.
B. This option is incorrect because it refers to the development of teeth, which is a separate process called odontogenesis and occurs independently of ossification.
C. This option is the correct answer, as it describes the ossification process during the seventh month of pregnancy for the secondary ossification centres.
D. This option is incorrect because it refers to the development of teeth, which is a separate process called odontogenesis, and occurs independently of ossification.

**Clinical Pearl:** A detailed understanding of fetal skeletal development is essential for understanding skeletal anomalies and congenital disorders, as well as interpreting radiographs and ultrasound findings in newborns and infants.