Which statement about skids and jackknife is correct?

1. A jackknife is when the tractor and trailer fold toward each other at the coupling.
2. This statement confuses the tested combination-vehicle rule with an unrelated CDL topic.
3. This answer would create an unsafe coupling, braking, turning, or inspection habit.
4. This choice is not supported by the Texas CDL handbook or FMCSA combination-vehicle standards.