Regarding Shigella:

Question $53$ options:

A$)$

Their classification into groups is based on the O antigen.

B$)$

The D serogroup $($Shigella sonnei$)$ accounts for over $2/3$ of the shigellosis in the U$.$S$.$

C$)$

They cause bacillary dysentery characterized by painful passage of low$-$volume stools containing blood and mucus.

D$)$

All of the above is true.

E$)$

A and C only.