The correct choice is A.
After the first days of the baby's development in its zygote stage, it remains in the mother's uterus as an embryo. It will remain in the uterus until it is born.
There are a few stages of embryo development:
1. Fertilization: this is where the female gamete (egg) meets with the male gamete (sperm) and they form a zygote
2. Blastocyst development: this is where the zygote divides into a ball of cells that eventually becomes the embryo inside a structure called the blastocyst; the blastocyst then travels up to the uterus.
3. Embryo development: this is where the embryo truly starts to develop in the uterus, growing the crucial body parts
i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.
all these collisions do one thing, and that thing is explained in the last option. when dusst, rocks and ice collide, they harden and form giant layers of rocks or hard ice.
d) to harden materials to form different parts of earth’s layers
hope it ,