在圆圈里填上“+”“-”“×” “+”。
(1)使计算结果最大。
7○7 8○3 4○1
(2)使计算结果最小。
7○7 9○3 4○1
(1)×,×,+; (2)-,÷ ,-
After a heated discussion, we suggested the customer _______ the product back for repairs.
A.to send
B.send
C.sends
D.sent
点火前炉膛必须以()的额定风量对炉膛及烟道通风。
A.20%-30%
B.25-35%
C.25%-30%
D.20-35%