单选题：The time complexity of the following piece of code is:

The time complexity of the following piece of code is:

int sum = 0;
for(int i=1;i<n;i*=2)
for(int j=0;j<i;j++)
sum++;




A.$$O(\log n)$$
B.$$O(n)$$
C.$$O(n \log n)$$
D.$$O(n^2)$$


答案：B