Given the typical range of $4\%$ to $7\%$ in net profit margins for dollar stores, how was the industry's profitability during $2008-2011$: low, moderate, or high? How does Porter's Five Forces model explain this profitability based on the level of competition in the industry? Net profit margin $=($net income $\frac{?}{?}$ net sales$)100$

$($No need to include calculations and specific numbers. Only a broad statement based on the data in the case will be sufficient as evidence for the first part of the question$)$