A regression is estimated relating to earnings to years of schooling. The data relating to earnings for different individuals who have completed their university education i.e. 16 years of education and they have no further education has been collected. Based on the given data, what OLS coefficient is expected to find. 

a). The coefficient is positive and significant 

b). The coefficient is negative yet insignificant 

c). The slope of the OLS estimator is zero 

d). As there is no variation in the data for the explanatory variable, the OLS slope estimator would not be defined.