Which statement best describes when a variable with missing data should be remedied with imputation?

Question $18$ Answer

a$.$

When a small number of observations are missing for the variable.

b$.$

When an alternative variable that is strongly related to the variable with missing data is not available to replace it$.$

c$.$

When the missing data occurs in a random fashion for a small number of observations are missing for the variable.

d$.$

When a significant number of observations are missing for the variable and deleting the variable will substantially improve the number of complete cases available for analysis.