Explanation:

The `Ctrl+=` key combination is a common keyboard shortcut in many word processing and text editing applications, such as Microsoft Word, Google Docs, and others. \nLet's analyze the effect of this shortcut: * **Subscript:** Subscript text appears slightly below the normal line of text and is typically smaller. It is commonly used in chemical formulas (e.g., $\text{H}_2\text{O}$) or mathematical expressions. The `Ctrl+=` shortcut is universally recognized for applying or removing subscript formatting. * **Superscript:** Superscript text appears slightly above the normal line of text and is typically smaller. It is used for exponents (e.g., $x^2$), footnotes, or ordinal indicators (e.g., $1^{\text{st}}$). The common shortcut for superscript is `Ctrl+Shift+=` (or `Ctrl++` on some keyboards). * **All Caps:** This formatting changes all selected text to uppercase letters. The shortcut for this is typically `Shift+F3` (to cycle through sentence case, lowercase, uppercase) or a specific menu option. * **Shadow:** This is a text effect that adds a shadow behind the text. It is usually applied through text effects or formatting options in the ribbon/menu, not a simple keyboard shortcut like `Ctrl+=`. \nTherefore, the `Ctrl+=` key combination is used to apply or remove subscript formatting. \nTherefore, the correct option is (B).