**Core Concept**
The sucking habit is a common oral habit that can affect the growth and development of the dental arch and facial structure. In orthodontics, sucking habits are categorized into vertical and horizontal growth tendencies based on their impact on the growth pattern of the maxilla.

**Why the Correct Answer is Right**
The sucking habit is more detrimental to vertical growth tendency than horizontal growth tendency. In vertical growth tendency, the maxilla grows downward and forward, whereas in horizontal growth tendency, the maxilla grows outward and forward. Sucking habits, such as thumb sucking, can lead to an increase in the vertical dimension of the face and a decrease in the width of the upper arch, which is more pronounced in vertical growth tendency. This is because the forces exerted by the sucking habit can cause the maxilla to grow downward, leading to a narrow upper arch and a long face.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because sucking habits are not more favorable in horizontal growth tendency than vertical growth tendency. In fact, sucking habits can still cause problems in both growth tendencies, but the effects are more pronounced in vertical growth tendency.

**Option C:** This option is incorrect because there is a specific effect of sucking habit that is more pronounced in vertical growth tendency than horizontal growth tendency.

**Option D:** This option is incorrect because there is a correct answer among the options, which is A.

**Clinical Pearl / High-Yield Fact**
It's essential to note that sucking habits can be a contributing factor to the development of Class III malocclusion, particularly in vertical growth tendency. Therefore, early detection and intervention are crucial to prevent or minimize the effects of sucking habits on the growth and development of the dental arch and facial structure.

✓ Correct Answer: A. Is less favourable in vertical growth tendency than horizontal growth tendency.