3. Four students take an exam, three of whom score $70, 80, 90$. If the average score of the four students is 70, then the score of the fourth student is ( ).
(A) 40
(B) 50
(C) 55
(D) 60
(E) 70
3. A.
$$
70 \times 4-(70+80+90)=40 .
$$