命题是断言某事是或不是事实的陈述。
A proposition is an assertion that something is or is not the case.
The novel is the most democratic of art forms because it requires only a reader.
It is the lives we encounter that make life worth living.
The best victories are the ones that seem impossible.
The first duty of the sovereign， that of protecting the society from the violence and invasion of other independent societies， can be performed only by means of a military force.
燃气发动机是所有热机中最完美的，因为它结合了蒸汽机和内燃机的优点。
Aquaculture is agriculture's next frontier.
数学是给不同事物赋予相同名称的艺术。