The given situation in the question where an Adenine nucleotide is swapped for a Thymine nucleotide, which as stated are complimentary of each other just like guanine and cytosine, can cause all three types of mutations, frameshift nonsense, frameshift missense and silent because the situation is not specific to either of them. There is no information whether the change resulted in a change in the amino acid structures or not. In this case the best answer is D.
Answer: Driven from their homes by unsatisfactory economic opportunities and harsh segregationist laws, many blacks headed north, where they took advantage of the need for industrial workers that arose during the First World War.
Ice ages have occurred in the earth history and do occur more or less regularly in a cycle. It is believed that ice ages are as a result of small changes in the earth's orbit and also dependent on the solar cycles. The temperatures on the earth reduce causing the ice sheets in the poles to extend to the subtropics.