The correct answer is option 'D' - word-break.

HTML Bullet Points:
- The CSS3 property 'word-break' can be used to allow line breaks within words.
- It provides control over how long words should be handled when they exceed the width of their container.

Explanation:

The 'word-break' property in CSS3 allows you to control how words are broken and wrapped when they exceed the width of their container. It provides different options to handle long words or strings of characters.

1. word-break: normal;
- This is the default value and it allows the browser to handle line breaks within words automatically.
- Words will not be broken at arbitrary points, but will wrap to the next line when necessary.

2. word-break: break-all;
- This value breaks words at any point, even if it is within the word itself.
- It allows long words to wrap onto the next line, breaking them at any character if necessary.
- This can be useful when dealing with URLs or long strings of characters.

3. word-break: keep-all;
- This value prevents word breaks within CJK (Chinese, Japanese, and Korean) text.
- It is commonly used for these languages to keep words together without breaking them.

The 'word-break' property can be applied to any block-level element or inline-block element. It is particularly helpful when dealing with responsive designs, where the width of a container may change based on the viewport size. By using 'word-break: break-all', you can ensure that long words or strings of characters are properly wrapped and displayed, rather than overflowing the container or disrupting the layout.

In conclusion, the 'word-break' property in CSS3 allows you to control how long words are handled when they exceed the width of their container. It provides options to break words at any point ('break-all') or to prevent word breaks within CJK text ('keep-all').