Select the most appropriate meaning of the given idiom.

An eye opener

A shocking revelation

The most appropriate meaning of the idiom "an eye opener" is a shocking revelation.

The other options are incorrect.

• "A tough decision" is not the same as an eye opener. A tough decision is a decision that is difficult to make, while an eye opener is a revelation that is shocking or surprising.
• "A difficult task" is not the same as an eye opener. A difficult task is a task that is hard to do, while an eye opener is a revelation that is shocking or surprising.
• "A small opening" is not the same as an eye opener. A small opening is an opening that is not very big, while an eye opener is a revelation that is shocking or surprising.

The idiom "an eye opener" comes from the idea of something that opens your eyes to a new reality. In the same way, an eye opener is a revelation that is shocking or surprising, and that changes your understanding of something. For example, you might say that the news of the terrorist attack was an eye opener for the world.