What are som important organ in the skeletal/muscular system?

The answer is a. the rock was made from more than one type of material.

It is a selective permeable cell membrane that allows only certain molecules or ions to pass through it by active or passive transport.

The answer to your question is the tricuspid valve

Event 1. a cataclysmic event initiated the collapse of the solar nebula.step 2. the temperature of the solar nebula began to increase, as it rotated faster and flattened into a disc.step 3. hydrogen and helium remained gaseous, but other materials would condense into solid "seeds."step 4. temperature differences in the nebula caused terrestrial planets to form closer to the center of the nebula and gaseous planets to form farther out.step 5. solar wind from the sun blew the remaining gas into interstellar space.