Necessary but not sufficient: q =>p but p! = & gtq(！ =>: I can't push it out, just draw a diagonal line in the middle).

Necessary condition: q =>p.

Think that the difference between the two lies in:

It is necessary to explain (or define) the logical relationship between P and Q, that is, whether P can deduce Q and Q can deduce P..

The necessary condition only shows that Q can deduce P, but there is no explanation or restriction on whether P can deduce Q. ..

Necessary and sufficient conditions are both necessary conditions. But by default, necessary conditions refer to the former (that is, necessary and insufficient conditions). Finally, I suggest that in order to avoid confusion, it is necessary to do the usual questions, especially the exam recommendation.