城市景观是什么最为明显的景观类型。（）
A．人为干扰
B．自然干扰
C．物质生产最高
D．系统最为稳定
参考答案：A
--- does your sister go skateboarding?
--- Every day.
A．How long
B．How many
C．How much
D．How often
背对背信用证开立后，原证即失去效用。
