Trisomy=3 chromosomes; 1 more than the required pair (2)
21=the type of chromosome
So, here we can eliminate A and B.
Now we have C and D.
I know that when sperm cell(s) simultaneously fertilize [an] egg, a class of identical twins will form. Therefore, we can eliminate D, leaving us with merely C. Henceforth, C is your final answer.
Explanation:
the last option is the correct answer
Explanation:
Sediment discharge was historically approximately 270 million cubic meters/year of suspended load and 130 million cubic meters/year of bedload. This has decreased 80% since 1850 and can be divided into three periods: historical period (pre 1900), pre-dam period (1932-1952), and post dam (1963-1982). Suspended sediment loads declined 43% between the historical and pre-dam and 51% from pre-dam to post-dam periods. The size of sediment also decreased drastically including a 72% decrease in the sand fraction. Most of this is due to dams on the tributaries acting as sediment traps primarily for the coarser sediments. Large-scale land clearing for agriculture contributed to increased sediment loads in the historic period.
The red-legged frog breeds in ephemeral ponds from January through March. Its relative, the bullfrog, breeds in permanent ponds from late March through May. There are two pre-mating isolation mechanism at play here,
1. Ecological isolation: The habitats are different, hence the individuals of both the species do not meet. Ephemeral ponds are temporary ponds that develop during rainy days, while the permanent ponds are full of water throughout the year.
2. Temporal isolation: The time of mating is different for both the species to avoid contact between the individuals of closely related species. Red-legged frogs mate in January to March slot and the bullfrog in the March to May slot.
