The assertion is TRUE as the context explicitly states: 'Cell lines derived from primary cultures of normal cells are finite cell lines.' However, the reason is FALSE. The context states that 'Some cells of the finite cell line undergo transformation and resume the ability to divide indefinitely, and become a continuous cell line.' The reason incorrectly uses the word 'retain' instead of 'resume' and fails to mention that these transformed cells become a continuous cell line, not a finite cell line. Additionally, the reason does not explain why cell lines derived from primary cultures of normal cells are finite; it describes a different phenomenon altogether - the transformation of finite cell lines into continuous cell lines.