Cell differentiation occurs when various genes are expressed to a different extent in different cells. what does it mean for a gene to be "turned off," or not expressed?

a. transcription into rna does not occur for that gene.
b. that gene is removed from the cell's dna.
c. the rna for that gene is not translated into protein.
d. the proteins sequenced by that gene are broken down inside the cell.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.