Which of the following is formed immediately after fertilization?
A: zygote

Hydrogen is located on the left side of the periodic table in the same column as the alkali metals, but it has characteristics of a nonmetal. Which of the following is a physical property of hydrogen?
A: Hydrogen is a gas at room temperature.

Which of these provides most of the oxygen in Earth's atmosphere?
A: ocean phytoplankton

The first microscopes were built in the 1600s. Microscopes have improved since then, but still perform the same job. How do microscopes most help scientists?
A:
They make small objects easier to see.