Final answer:
The true statement is that there have been multiple ice ages over the past half billion years. The Pleistocene Epoch saw significant glaciations, but it was not the first ice age our planet experienced. Humans lived during the last ice age, but dinosaurs were long extinct by then.
Step-by-step explanation:
The correct statement is b) Extremely cold periods with ice ages have occurred a number of times over the last half billion years. Scientists have found evidence of at least five significant periods of cooling on the planet, commonly known as ice ages, each including multiple glaciations where glaciers grew on land. These periods were mainly due to changes in the tilt of Earth's rotational axis caused by the gravitational effects of other planets. The most recent glaciation period began about 100,000 years ago, peaking around 18,000 years ago, and the ice age it was a part of ended approximately 12,000 years ago. During the last ice age, humans did inhabit the Earth, but dinosaurs had been extinct for millions of years prior to this period.