杀虫的方法很多，下列哪种方法杀虫最彻底（）
A、物理方法
B、生物方法
C、环境防治法
D、化学方法
参考答案：C
I had never seen so many people with so many disabilities. I returned home, silently （）. thinking how fortunate we really were.
A．retrospective
B．introspective
C．perspective
D．prospective
