The phrases that are gerund phrases are option A and C. 
A. A healthy lifestyle requires getting regular exercise. 
C. Watching too much television may contribute to depression. 
A gerund is a noun formed with a verb ending in -ing. 
A gerund phrase always start with gerunds, includes modifiers and often include other objects. In addition, a gerund phrase always functions as a noun, and are always subjects, objects, or subject complements in sentences. 
For example, 
A healthy lifestyle requires getting regular exercise.  
Watching too much television may contribute to depression. 
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