External fertilization is the correct answer.
every cell has work to do but different cells may have different jobs in multicellular organisms, cell with the same type of job often work together. These group of specialized cell from tissue in turn, tissue often group together to form larger units called organs the heart is an organ; so is the stomach.
The natural spreading of particles through a liquid or gas is called diffusion
Calcium oxide based on the above explanation is an ionic compound.
