$\frac{1}{3}$

$\frac{1}{6}$

$\frac{1}{2}$

$\frac{1}{8}$

C. $\frac{1}{2}$

Total cases are = 2*2*2 = 8, which are as follows

[TTT, HHH, TTH, THT, HTT, THH, HTH, HHT]

Favoured cases are = [TTH, THT, HTT, TTT] = 4

So required probability =$\frac{4}{8}=\frac{1}{2}$