What do the numbers on the ph container stand for?

Why do you need to classify the size of a particle

Feedback is given with little or no reservation 1.supportive 2.high-monitoring 3.positive 4.low-monitoring ?

Which statements about the two fossil images are correct? 1. cave bears are ancestors of plateosaurus. 2. plateosaurus were present on earth before ostracoderms. 3. ostracoderms were the first to die. 4. plateosaurus died after the ostracoderms. 5. cave bears are the oldest fossils.