Step-by-step explanation:
come on ! just use common sense. you do understand English, yes ?
a problem and a solution. that's what we are looking for.
let's start with the last one :
Because of severe drought in the area, this year’s harvest has been dramatically lower than normal.
yes there is a problem, but is there a solution ? no. there is only a consequence. or a problem and it's reason. but knowing the reason for a problem is not a solution. nothing is introduced to the situation as a solution.
the next one :
Compared to 2020, the 2015 school year was virtually problem-free.
just a statement. no problem, and therefore also no solution.
the next one :
Because the island is so far from the mainland, the people have to wait for needed supplies.
that is practically the same as in the first one. there is a problem and its reason. but nothing about a solution.
and finally :
When my cousins come to visit, we put an extra leaf in the table to make it bigger.
a solution is described right away with the description of what problem it solves.
that is what you are looking for.
what was your actual problem that we just solved ?