以前写过金星西大距。天文学上的大距，指的是在地球上观测地球与太阳之间的行星，相对于太阳位置关系。东大距与西大距，都是水星与太阳相对位置关系变化过程中的一个特定时刻。这一时刻，太阳与水星的视角距离最远。大距前后的一段时间，更适合水星观测。 大距这一概念 ...

When a large number of people head toward the same exit from an event venue or building, people can become congested near the ...

Factory equipment and machinery can fail if used for a long time.However, repairing equipment every time it breaks down leads ...