Please help me with my hw, explanation appreciated!

The plots below show the histogram of residuals as well as the residuals versus fitted values plot (rvfplot) for Model 3 (which includes covariates of HDI category, years of schooling category and measures of disease immunization and morbidity (polio, diphtheria, and HIVAIDS mortality). Which of the linear regression assumption(s), if any, appears to be substantially violated, based on these plots? Feed rates a. Normal distribution b. Equal variances c. None of the assumptions appears to be substantially violated d. Independence of observations