B is correct because creating an HA setup with a second FortiDDoS 200F will provide redundancy in case one of the devices fails. This will prevent all traffic from being dropped in the event of a failure.

D is correct because the FortiDDoS 1500F has a larger throughput capacity than the FortiDDoS 200F. This means that it will be less likely to drop traffic even under heavy load.

The other options are incorrect. Option A is incorrect because changing the Adaptive Mode will not prevent the device from dropping traffic. Option C is incorrect because moving the internet connection from the SFP interfaces to the LC interfaces will not change the throughput capacity of the device.

References:

FortiDDoS 200F Datasheet | Fortinet Document Library

FortiDDoS 1500F Datasheet | Fortinet Document Library

High Availability (HA) on FortiDDoS | FortiDDoS / FortiOS 7.0.0 - Fortinet Document Library