This[usage-this]

This。代词this若指代前一句或子句的完整意思，未必总能承担这一重负，因而可能产生不精确的表述。

• 误：Visiting dignitaries watched yesterday as ground was broken for the new high-energy physics laboratory with a blowout safety wall. This is the first visible evidence of the university's plans for modernization and expansion.
• 正：Visiting dignitaries watched yesterday as ground was broken for the new high-energy physics laboratory with a blowout safety wall. The ceremony afforded the first visible evidence of the university's plans for modernization and expansion.

在上面左栏的例子中，this并不能立即说明什么是"第一项可见的证据"。