答案为 B。句意为：他把所有东西都锁在保险箱里以防万一。

1. take the precaution of doings sth

其字面意思是：采取了做某事的预防措施（of doing sth 为后置定语），通常译为“为保险起见而做某事”“做某事以防万一”等。其中的 precaution 通常用单数，且其前通常有定冠词。如：

I took the precaution of insuring my camera. 我给我的照相机投了保，以防万一。

He had taken the precaution of seeking legal advice. 为保险起见，他寻求了法律援助。

I took the precaution of turning the water supply off first. 我先关闭了供水系统，以防万一。

She took the precaution of packing extra medicine for the trip. 她这次旅行多带了些药，以备不时之需。

I took the precaution of clearing out my desk before I left. 为了保险起见，我离开前清理了我的桌子。

2. take precautions to do sth

其意为：为了做某事而采取预防措施。其中的不定式为目的状语。这样用的 precaution 通常用复数形式。如：

Vets took precautions to prevent the spread of the disease. 兽医们为防止疾病蔓延采取了预防措施。

She took precautions to prevent anyone from reading her computer files. 她采取了措施以防别人阅读她的计算机文件。

They failed to take the necessary precautions to avoid infection. 他们未能采取必要的预防措施来避免感染。

You must take all reasonable precautions to protect yourself and your family. 你必须采取一切合理的预防措施，保护自己和家人。

Doctors recommend taking precautions to protect your skin from the sun. 医生建议采取预防措施，以避免皮肤在太阳下曝晒。

有时也用take every precaution to do sth，意思更强调，指采取一切预防措施做某事。如：

We take every precaution to avoid accidents. 我们采取一切预防措施避免事故发生。

We take every precaution to ensure that you have a comfortable journey. 我们采取一切措施确保您旅途舒适。