This is an Inference Question so it is specific (asks about a detail) and implied (you must draw conclusions based on the passage but avoid answers which include what is directly STATED).

The detail we need to look at can be found in line 58. In order to answer the question correctly, you need to perform the Initial Reading - read 1 or 2 sentences from each paragraph and all sentences that include the contrast words like "however," "but", etc.

We learn from the Initial Reading that:
Para 1 - 10% of black population left the South
Para 2 - analysis who left - people moved first from rural areas to the cities in the South and then maybe the same people moved from the South to the North
Para 3 - over 30% were skilled workers, over 60% worked in new industries
The "easy conclusion" connected the problems that the migrants had in the North to their rural background. However, we learn from the sentences around the line 58 that the two could have been completely unrelated since the unemployment was high due to the high number of workers and not to their lack of appropriate skills. Now, we need to find an assumption that will support the "easy conclusion."

A - This statement is too general and does not provide support for the hypothesis that rural background is an obstacle in being successful after the move to the North
B - This statement is also out of scope, we don't really care whether migrants come back to rural areas
C - correct, this statement shows that rural background can stop one from achieving financial success in the city
D - incorrect, it is not important what jobs migrants want to perform, the "easy conclusion" points to the fact that they generally LACK skills appropriate to get a job in the city
E - incorrect, we are not interested in the second migration - it is not mentioned