Before DNA replication, how many molecules of DNA make up a chromosome?

Figure 7 The number of DNA molecules in a chromosome: (a) a chromosome prior to replication contains a single DNA molecule; (b) a chromosome that has been replicated and consists of two chromatids, each comprising a single DNA double helix molecule.

Explanation:

the answer is: they occur when the sun, moon, and earth are aligned. in spite of their name, these tides occur twice a year in the spring and fall.

explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.