Dna and rna share a number of similarities, but they also differ in certain aspects of their structure.
which nitrogenous base is found in rna but is not found in dna?

Uracil is the nitrogenous base that exists in RNA but is absent in DNA.

Explanation:

Uracil or uracil is a nitrogenous base. Represented by the letter U in the genetic code, it is a simple, pyrimidine ring base capable of making two hydrogen bonds, just like thymine. It replaces thymine in DNA to RNA transcription to complement adenine. It is an exclusive base of RNA, that is, it does not occur in DNA.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.

the two answers are a, the population of birds with large beaks will increase on the island, and c, the trait for large beaks will be passed on to future generations through natural selection. the reason for that is because if the birds that have beaks developed for eating small seeds lose all of their food, they will go hungry and eventually starve because they physically cannot eat the large seeds, therefore making the population of large beaked birds higher. also, if the trait of large beaks are dominant on the island over small beaks, then over time the large beaked birds will reproduce more and more, while the smaller beaked birds will reproduce less and less because they can't survive with the food provided. that leads to the trait of small beaks disappearing and the trait of large beaks taking over the island.