First, can we form a set?

1, yes.

2. no.

3. yes.

4. no. This is a set of numbers, but I'm not sure.

Second, enumerate the collections.

1、{0, 1,2,3,4,5}

2、{-2,3}

3、{……-3,-2,- 1}

Third, describe the set.

1 、{ x l lxl & gt3}

2 、{x l x？ +4 & gt； 2}

3.{xlx = 2n+ 1, where n is a natural number, 1≤n≤4}

4.{ Full parallelogram}