The average duration of human pregnancy is approximately ........... months.

What is the average nine-month period of human pregnancy called?

After one month of pregnancy,the embryo's $A$ is formed. By the end of the $B$ month of pregnancy,the foetus develops limbs and digits. By the end of $C$,most of the major organ systems are formed,for example,the limbs and external genital organs are well-developed. By the end of $D$,the body is covered with fine hair,eyelids separate,and eyelashes are formed. Here $A$ and $D$ refer to:

The formation of the segmentation cavity indicates:

In a urine analysis,the presence of which of the following indicates pregnancy?

The ratio of the nucleus to cytoplasm at the beginning of cleavage is