You are able to fluorescently label a cell in a chick embryo and watch it over the course of a few days. On the first day, the cell looks like most others around it, but over time, you notice that it fuses with other cells and elongates to form long multinucleated tubes. What best describes the process you have observed?

A. differentiation
B. commitment
C. determination
D. specification

Cell differentiation consists of a set of processes that transform and specialize embryonic cells. After these transformations, their morphology and physiology are defined, which make them capable of performing a certain function.

We call differentiation in biology the process that all living cells go through to specialize in a particular function. These cells, despite being differentiated, continue with the same genetic code as the first cell, and the difference between them is in inhibiting or activating certain groups of genes - these responsible for defining the function of each of them. This, in addition to determining its function, entails some changes in cell structure, as happened with the cell described in the question, which promoted a change in its structure by merging with neighboring cells to form a multinuclear tube.