导线压接后导线端头露出长度，不应少于（），导线端头绑线应保留。
参考答案：20mm
－_____ you _____ to Beijing yet?
－Yes, I _____ there last year.[ ]
A. Did, go; went
B. Have, gone; have been
C. Have, been; have been
D. Have, been; went
