试题选项中图形符号表示信号器件是(____)。
A<img src="/tupian/shandong/dinghongjian/dinghongjian24.jpg"/>
B<img src="/tupian/shandong/dinghongjian/dinghongjian17.jpg"/>
C<img src="/tupian/shandong/dinghongjian/dinghongjian25.jpg"/>
D<img src="/tupian/shandong/dinghongjian/dinghongjian18.jpg"/>