Immigration is when people move from a particular country into another country so as to improve their standstill of living, further their education or have better job opportunities.
Immigration wall is the barrier between a particular country and another country which is done so that illegal migration can be prevented. A good example is that of the United States and Mexico.
A good topic sentence about the immigration wall is "Effects of immigration wall to the development of an economy".
I believe the sentence that is off-topic is Sentence 3 The gardeners also decide what types of pesticides, if any, are used on the produce in the garden hope this helps :)
