More than one relationship can be created between two activities

Dear Team,

Recently I start to get familiar with Project Builder (CJ20N).

When I create network activities, it is found that multiple relastionships can be created between the same two activities.

As I think, normally there should be only one relationship type between two tasks in project planning.

But I'm not sure why multiple relationships can be created in SAP PS.

Can I restrict that only one relationship can be created between two activities?

Please tell me whether there is any solution available.

Thanks and regards,

Kila