Which of these is an example of asexual reproduction?
new grass plants grow from grass runners that spread across a lawn.

the leaf of an african violet is placed on the ground and a new plant grows from it.

a piece of a rose stem is planted in the ground and a new rosebush grows there.

all of the above

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.