# Multiple Choice Questions

+ Which of the following statement(s) is/are correct for the system variables?
  + A. System variables have scopes.
  + B. You may change the system variables via MySQL clients.
  + C. The modification on SESSION system variables will only take effects after re-connections.
  + D. The modification on GLOBAL system variables will not impact current session.

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+ Answers: A B
+ C is wrong. The modification on SESSION system variables take effects immediately.
+ D is wrong. The modification on Global Persistent System Variables will impact current session (e.g. tidb_gc_enable)