Answer:
The correct answer is option A. "Heart".
Step-by-step explanation:
It is well documented that just about 17 days after conception, the human heart starts to beat. This happens because heart cells starts to develop about 17 days after fertilization. Particularly, the cells called cardiomyocytes, which trigger the cardiac muscles contraction needed to start the heartbeat. Actually, the heart is the first organ to form during embryogenesis.