The group of thumb sucking in which the thumb do not contact the lower incisors, according to Subtleny et al:: (A) Group I, (B) Group II, (C) Group III, (D) Group IV
Answer is C. Subtleny et al (1973) noted four types of thumb-sucking depending upon the

Amount of pushing of tongue inside the oral cavity
The contact between the thumb and the palate 
The contact between the thumb and anterior teeth.