China Naming Network - Eight-character Q&A - 100, of which 20 are first-class, 30 are second-class and 50 are third-class, and 20 are selected as samples. ① Random sampling method: draw lots.

100, of which 20 are first-class, 30 are second-class and 50 are third-class, and 20 are selected as samples. ① Random sampling method: draw lots.

From the differences and connections of the three sampling methods:

The above three methods are all feasible,

And all three sampling methods are equal possibility sampling.

That is, the probability of each individual being drawn is equal to 20 100 = 1 5.

So choose a.