E(X)=1·1/4+2·1/3+3·1/6+4·1/4=29/12
E(X²)=1²·1/4+2²·1/3+3²·1/6+4²·1/4=85/12
D(X)=E(X²)-[E(X)]²
=85/12-841/144
=179/144
【答案】选C