•observation
•smell
•touch
•they also look at the plant and see the features or the characteristics
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Answer:
(A) The variation resulting from meiosis and the union of gametes means some individuals will have a chance of colonizing diverse distant environments successfully.
(D) Vegetative propagation is more efficient than sexual reproduction when the current generation is well adapted to the local environment.
Explanation:
Sexual or asexual (options B and C) are not a "last ditch", it pretty much depends on the type of organism and its strategy for survival. There are thousands of organisms that can reproduce either sexually or asexually depending on the environmental conditions.
Option A. Genetic variability is important because sometimes the genetic variability produce during the sexual reproduction processes (crossing over, chromosomes assortment and DNA from 2 parents) can confer an organism the adaptability mechanism to thrive in different environments.
Option D. Since asexual reproduction delivers genetical equal organisms, the offspring is already adapted to local conditions and can colonize at a faster rate.
Although the actual questions are missing from your ask, here's how you can tell.
If the study will be messed up (added bias) through interaction with the subjects the study should be observational. For example if a biologists wanted to study the eating habits of wild birds in the tropics, they would need to do an observational study. if they did a controlled experiment, the birds will change their eating habits based on human interaction, thus making the study invalid.
If the study requires specific measurements, close monitoring, or contact and interaction with the subjects the study should be a controlled experiment. For example, if a scientist wanted to test out a new drug, the health of patients would need to be closely monitored.