to be total strangers (idiom)
素 · 10 strokes
Depicts raw silk (糸) hanging from a rack.
不 · 4 strokes
Pictograph of sepals of a flower. The modern meaning "no" is a phonetic loan.
相 · 9 strokes
Depicts an eye (目) looking at a tree (木). Based on the original meaning "look at". The meaning of this character has shifted over time to "compare" and "each other".
识 · 7 strokes
Simplified from 識. Phonosemantic compound. 讠 represents the meaning and 只 represents the sound.
我们两个素不相识，你为什么要帮我？
We are total strangers, so why would you want to help me?