Questions

Crystal size in igneous rocks is determined by rate of cooling i.e, the time taken by magma to cool down. 

Hence, the slower the rate of cooling the larger the crystals. The faster the rate of cooling the smaller the crystals.

The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms.

Amphibians are one of the most sensitive groups to change, whether that is caused by habitat loss, invasive species, disease, trade or climate change. Their sensitivity to environmental threats has been generally linked to the observation that amphibians are characterized by a rather permeable skin. Given their complex life cycles and other traits, amphibians are often recognized as indicators of ecosystem health.

I am History.

Yes, history refers to all the past, but we can create history in the presentand it cannot be polluted in the future.