Sexual reproduction relies on two different sexes (female & male) because one has the egg and the other has the sperm.
Answer:
A. Compounds contain fixed ratios of different elements.
Explanation:
Water always has this 2:1 ratio of hydrogen to oxygen. Like water, all compounds consist of a fixed ratio of elements. It doesn't matter how much or how little of a compound there is. It always has the same composition.
By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory. The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells.
