The period of the embryo begins at and ends with which takes about ) conception; birth; nine monthsb) the first trimester; implantation into the uterine wall; twelve weeksc) week 3; formation of bone cells; six weeksd) organogenesis; ossification; one trimester

a) conception; birth; nine months

Explanation:

The period of the embryo begins at conception and ends with birth, which takes about nine months.

An embryo is formed when the male and female gamates meet in the process of fertilization, this is called conception. The pregnancy last for about nine months and ends with the birth of a child.

  b.

there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.