题目

 Everyone in the village knew him, so we had _______ his house. A. no difficulties to find              B. some difficulties in finding C. no difficulty to find                 D. no difficulty in finding 答案：D如图所示的电路中，只闭合S1、S2时，灯L1、L2是 ______ ，只闭合S3时，灯L1、L2是 ______ ．（填“串联”或“并联”）