¶1—Judgment, Supreme Court, New York County (Felice K. Shea, J.), rendered October 12, 1990, convicting defendant, after a jury trial, of criminal sale of a controlled substance in the third degree, and sentencing him, as a second felony offender, to a term of 4x/i to 9 years, unanimously affirmed.
¶2The trial court did not err in closing the courtroom during the undercover officer’s testimony since the officer indicated *132that he continued to work in the specific area involved in this case and that exposure of his identity would compromise his safety and the effectiveness of his work (People v Okonkwo, 176 AD2d 163, lv denied 79 NY2d 862). In any event, the courtroom was empty, and defendant declined the opportunity extended by the court to request that particular persons be allowed to enter. The trial court properly allowed the undercover’s background testimony concerning the procedures in buy and bust operations, since such information helps the jury to understand the officers’ behavior in those operations (People v Kelsey, 194 AD2d 248, 252). Testimony concerning possible reasons why prerecorded buy money is not found on a suspect was admissible since defendant made the absence of such money on his person a central issue in this case (supra, at 252-253). Defendant’s remaining contention is unpreserved for appellate review by appropriate objection and we decline to review it in the interest of justice. Concur—Sullivan, J. P., Wallach, Ross, Rubin and Tom, JJ.