I think the hydra lacks the specialized cells for touch and chemical detection. On the other hand earthworms have touch, light, vibration and chemical receptors along the entire body surface. Both of them are invertebrates (those animals without a backbone), they include insects, worms, jelly fish, spiders among other animals.
Animals have so many different enzymes to digest their food they eat variety of food in their diet so specif enzymes are needed to digest each type of food
The answer is: A. collecting data
During this process , researchers would use their observational skills and record every notable occurrence that happen to the variables.
The focus on this process is simply to add all relevant data without making any analyzation. That process come later on after the researchers started to change the variables in order to see whether it would create a correlation.
Changes in the state of matter A, bubbling or fizzing B, and changes in volume F
Hi unequal pupils would likely indicate a brain injury.
Hope this helps.