<human>: Here is a goal: How do I write my friend a message on the sidewalk outside of his house?

Which way makes more sense to accomplish this goal?

OPTIONS:
- use a piece of white chalk to write the message so it won't be permanent.
- use a strong spray paint to write the message so it won't be permanent.
<bot>: use a piece of white chalk to write the message so it won't be permanent.