若 $x,y$ 满足 $\{\begin{array}{l}x\ge 0,\\ y\ge 0,\\ y\ge x+1,\end{array}$  则 $x-2y$ 的最大值为____．

    Facebook CEO Zuckerberg just had a baby girl named Max, and to honor the occasion, he's giving away the majority of his wealth. In the letter____(write) by Zuckerberg and his wife, Priscilla Chan, to____(they) new baby girl, he announced the birth of his first child and the____(create) of the Chan Zuckerberg Fund，____will focus on curing disease, connecting people and____(build) strong communities.

    “For your generation to live in____better world, there is so much more our generation can do,” Zuckerberg wrote. “Today your mother and I are committing to spend our lives doing our small part to help solve these challenges.” The couple____(donate) nearly all of their Facebook stock to the cause. “We will give 99% of our Facebook shares-currently about $45 billion-to advance this____(value) mission,” he wrote. “We know this is a small contribution compared____all the resources and talents already working on these issues. But we want to do____we can, working along with many others.”

入连云栈^①

清·沈廉

飞栈盘空乌路分，烟复雾树合氤氲。

入缘蚁垤^②纷相引，风递猿声断更闻。

百道争飞天外瀑，千峰乱插马头云^③。

身当绝境浑忘险，不觉频穿虎豹群。

【注释】①连云栈：栈道名。在陕西汉中地区，古为川陕之通道，即所谓“蜀道”。②蚁垤（dié）：蚂蚁洞口的小土堆。③马头云：云的一种。

下列关于第一次世界大战爆发前的各大国关系的表述，不正确的是(　　)