B translates to: Take out a sheet of paper. Sacar is conjugated as ellos/ellas/Uds. in the subjunctive (Saquen).
C translates to: Raise your hand. Levantar is conjugated as ellos/ellas/Uds. in the subjunctive (Levanten).
D translates to: Repeat, please. Repetir is conjugated as ellos/ellas/Uds. in the subjunctive (Repiten).
E translates to: Open your books. Abrir is conjugated as ellos/ellas/Uds. in the subjunctive (Abran).
The answer is A. Siéntense (plural form) translates to sit down.