Which of the following brake fluids are glycol-based and can be mixed if necessary, and which must NEVER be mixed with them?

1. DOT 3 and DOT 4 are glycol-based and can be mixed; DOT 5 is silicone-based and must NEVER be mixed with them.
2. DOT 4 and DOT 5 can be mixed freely; DOT 3 must never be used in disc brake systems.
3. DOT 3 and DOT 5 are glycol-based and can be mixed; DOT 4 is mineral-based and must never be mixed with them.
4. All DOT ratings represent identical chemical compositions and can be mixed without restriction.