Is there a way for plugin "A" to ckeck that plugin "B" is activated?

Hello,

First of all, I ask you to forgive me for my English. I try to write as well as possible, but I know that it's not perfect.

Plugins may have dependencies. For example: Plugin "A" needs plugin "B" to be activated, in order to work properly.

Is there a way for plugin "A" to ckeck that plugin "B" is activated?

Thank you,

Denis