The correct answer is C. A/B Testing, as explicitly identified in the study guide.
The UX Designer already has two interface variants and a clearly measurable outcome: the number of completed contact forms. That is precisely the type of comparison the study guide associates with A/B Testing.
In an A/B test, different groups of users encounter different versions of an interface. The team then compares a predefined behavioral metric between those variants. Here, the metric is straightforward: which landing-page design produces the greater number or rate of form completions.
Option A, Eyetracking, would provide information about where users direct their visual attention. It could reveal whether they notice the form or other content, but it does not directly answer which version produces more completed forms at scale.
Option B, Field Studies, investigate users in their real environment and are useful for contextual understanding. They are not the most direct method for statistically comparing two high-traffic landing-page variants.
The presence of several thousand visitors strengthens the suitability of A/B Testing because the designer has sufficient traffic to compare observable behavioral outcomes between alternatives.
Study Guide reference/topics: A/B Testing, comparative testing, conversion measurement, behavioral metrics, Testing.
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