Answer:
In the first step of meiosis I, the chromosomes/genetic material of the cell condenses into a visible form, into a form called heterochromatin. The nucleolus also disappears.
In the second step, a process called synapsis occurs. This is when homologous chromosomes align themselves, gene by gene.
In the third step, crossing over occurs. Segments of corresponding DNA are cut and exchanged between non-sister chromatids of the formed tetrads.
In the fourth step, the nucleus fragments, the nuclear envelope fragments, the two centrosomes (if we're talking about an animal cell) separate from each other as their asters and mitotic spindles (mostly microtubules (kinetochore and non-kinetochore) lengthen. The microtubules extending from the centrosomes can now connect to chromosomes.
The answer would be C, "The earth is heated by terrestrial radiation."
Terrestrial radiation is a factor in what heats up the earth and it's a major factor in the study of global warming.
