The organ that becomes fully functional during the first trimester is the heart
Answer: Option A
Step-by-step explanation:
The gametes which are formed by meiosis fuse with each other to form the zygote , the homozygous gametes join together to form the heterozygous zygote. This zygote which is a single cell undergoes mitotic division to form the blastula.
The cells at this stage are non-differentiated; these cells later differentiate into different organs and develop a full grown organism. The development of organs in a human body is sequential and thus among the above the heart develops in the first trimester.