Analogy completion — choose the best word to complete the relationship: snow : mountain : ski :: warmth : lake : __

Introduction / Context:
This analogy links a setting, a condition, and an activity. In cold, snowy mountain settings, a typical recreational activity is to ski. In a warm lakeside setting, the parallel recreational activity should be selected to preserve the same situational logic.

Given Data / Assumptions:

• snow → mountain → ski (condition → place → activity).
• warmth → lake → __ (condition → place → activity).
• We must choose an activity naturally associated with warm lakes.

Concept / Approach:
Map each triad element to its role, then substitute a realistic, common activity for the second scene. 'Swim' is the most immediate and widely associated activity with warm lakes. Other candidates either describe materials, consequences, or broader concepts rather than an activity parallel to 'ski.'

Step-by-Step Solution:

Verification / Alternative check:
Consider frequency and directness: people commonly go to warm lakes to swim. While sailing or boating can also occur, 'swim' most directly mirrors the personal, body-centered activity of 'ski' in the first half. The other options do not function as activities in the same way or are not as prototypical.

Why Other Options Are Wrong:

• sand: a material, not an activity; better associated with beaches than lakes.
• sunburn: an undesirable consequence, not an activity.
• vacation: a broad event, not a specific action at the lake.
• sail: possible but less universally tied to lakes than swimming; also requires equipment.

Common Pitfalls:
Choosing a word tied to water but not an activity (e.g., 'sand'). Ensure the grammatical and semantic role matches 'ski' as an action verb.

Final Answer:
swim