Can't add interfaces into WAN LLB
My fortigate is FG200D, version is v5.4.1,build1064 (GA) . I have two leased lines and two ADSL circuit, I've finished the configuration of the ports show in the below picture . And I've configured four static routes for each wan port and policies.

When I want to add them into WAN LLB, I can't see them in the list show in the below picture

Who can tell me what's wrong with my configuration so that I can't add them into WAN LLB.
I hope configure a static monitor like SLA and track, how can I do? Thanks.