Which example best represents an expensive expression?

The best representation of an expensive expression is found in multi-step dot paths and collection methods. This type of expression often involves navigating through a sequence of objects or collections, which necessitates multiple lookups or calculations. Each step in the dot path can incur its own computational cost, especially when dealing with large data sets or complex object hierarchies.

In contrast, simple string comparisons, basic mathematical operations, and conditional statements are generally less resource-intensive. Simple comparisons typically involve straightforward equality checks, basic math operates with direct calculations, and conditional statements, while they may introduce some complexity, do not inherently require the extensive resource use that multi-step dot paths and collection methods demand. Thus, the complexity and potential overhead from traversing multiple object properties or applying collection methods make option B the most costly in terms of computational resources.