Which of the Following Production Functions Exhibits Increasing Returns to Scale

Which of the following production functions exhibits increasing returns to scale?

A) $Y = K ^ { 1 / 2 } L ^ { 1 / 2 }$
B) $Y = K ^ { a } L ^ { 1 - a }$
C) $Y = K ^ { 1 / 3 } L ^ { 2 / 3 }$
D) $Y = K ^ { 1 / 2 } L ^ { 3 / 4 }$
E) All of these answers are correct.