to keep secret

• 保密文件

  classified documents

• 保密工厂

  secret factory

• 保密车间

  secret workshop

• 保密机关

  intelligence agency

• 严格保密

  keep strictly confidential

• 绝对保密

  be strictly confidential

• 不再保密

  be no longer classified

• 在保密单位工作

  work in a secret department

• 这件事要保密。

  This matter must be kept confidential.