New technology was used in teaching. As a result, not only ______, but students became more interested in the lessons.

A．saved was teachers’ energy

B．was teachers’ energy saved

C．teachers’ energy was saved

D．was saved teachers’ energy

根据《城市天然气设施管理、运行、维护和抢修安全技术规定》，对用户户内安全检查每年不少于1次，并做好检查记录，在可能的情况下请用户签字认可，请问户内检查内容有哪些？（至少说四点）