Which types of isomers of $C_4H_8$ are possible? Give their names and structures.

(N/A) The isomers of $C_4H_8$ (degree of unsaturation = $1$) can be classified as follows:
$1$. Chain Isomers:
- $But-1-ene$ $(CH_3CH_2CH=CH_2)$
- $2-Methylprop-1-ene$ $(CH_3C(CH_3)=CH_2)$
$2$. Position Isomers:
- $But-1-ene$ $(CH_3CH_2CH=CH_2)$
- $But-2-ene$ $(CH_3CH=CHCH_3)$
$3$. Geometric Isomers:
- $cis-But-2-ene$
- $trans-But-2-ene$
$4$. Cyclic Isomers:
- $Cyclobutane$
- $Methylcyclopropane$