Final answer:
The last glaciation period began around 100,000 years ago and reached its peak about 18,000 years ago.
Step-by-step explanation:
According to the provided information, there have been several glaciations during the last 2.58 million years. The most recent glaciation period began around 100,000 years ago and reached its peak about 18,000 years ago.
This means that the answer to the first part of the question would be either (B) 5 or (C) 6 glaciations. However, the exact number of glaciations within this timeframe is not specified in the provided information.