符号FefS代表（）。
A、全部实芯焊丝和碳钢焊条
B、全部药芯焊丝和焊条
C、全部实芯焊丝和药芯焊丝
参考答案：C
He didn't realize he had forgot his bag _____ the plane had taken off.
A．unless
B．until
C．if
D．or
在自我评价过程中形成性自我评价属于哪个时间段?()
A．学年开始前
B．学年开始后
C．学年结束时
D．学年总结会召开时
