开膛手杰克的身份仍然是一个未破解的谜团。

The identity of Jack the Ripper remains ___an ___unsolved mystery.

许多环境问题仍未得到解决。

Many environmental issues remain ___unsolved.

1995年的那起谋杀案至今仍是悬案。

The murder case from 1995 is still ___unsolved.