ですから
desukara

Conjunction

1. so; therefore; accordingly; consequently; on those grounds; that is why; for that reason

Polite
Related to だから
いいえ、結構 けっこうです。お なか一杯 いっぱいですから。
iie kekkōdesu. onakaga ippaidesukara.
No, thank you. I've had enough.