这座老城区的道路系统是一个复杂的网络。

The road system in the old city was a ___complex network.

这部电影的情节太复杂了，我跟不上。

The film's plot was so ___complex that I couldn't follow it.

修改这个实验的结果是一项非常复杂的操作。

Modifying the results of the experiment was a very ___complex operation.