【判断题】A preview statement is usually necessary in the introduction even when a speaker is addressing an audience that is well-informed about the topic.
【简答题】What is a preview statement?
【判断题】What is a preview statement? Preview statement is a statement that indicates when the speaker has finished one thought and is moving on to another.
【判断题】判断一个集合是向量空间需要验证:集合是一个非空集合以及集合对于加法运算和数乘运算具有封闭性。