What is the best definition for the Thumb$-2$ instruction set?

Unlike the Arm instruction set, which is $32-$bit, Thumb$-2$ is a combination of $16-$bit and $32-$bit instructions that is a subset of the previous Arm instruction set that achieves

almost the same performance at a better code density.

Unlike the Arm instruction set, which is $16-$bit, Thumb$-2$ is a $32-$bit instruction set that is a superset of the previous Arm instruction set to provide better performance.

Unlike the Arm instruction set, which is $32-$bit, Thumb$-2$ is a $16-$bit instruction set that is a subset of the previous Arm instruction set to provide better code density

Like the Arm instruction set, which is $32-$bit, Thumb$-2$ is a $32-$bit instruction set that is a subset of the previous Arm instruction to provide better code density.