Answer: True
Explanation:
Buying enough negatively correlated stock can indeed help in diversification of a Portfolio and this on its own is very important as it reduces risk. The type of risk that it reduces however is Unsystematic risk. This is the unique risk inherent in owing stocks.
Systematic risk which is also called undiversifiable risk however cannot be so easily eliminated. This risk is inherent in the Market or the Market segment in question and results from a mix of the Economic, Geo-political and Financial factors in the market. As such, it will not be possible to eliminate all systematic risk.