I called the police at once（改为同义句）

题目

I called the police at once（改为同义句）
I （ ）a call （ ） the police at

答案

I called the police immediately.
at once 立即、立刻=immediately
按你给的格式是：
I (made) a call (to) the police at once.
call sb.= make a call to sb.