Alg. Efficiency

In Unit 10, the slideshows indicate that the number of inputs correlates to the number of bits it takes to represent that number in binary. Which gives you how many steps the binary search has. But in this question, why is the answer 7 and not 8 since 128 requires 8 bits. Does it not work all the time? See question:
A software engineer is testing a data structure that contains 128 sorted integers. Which of the following is closest to the maximum number of elements that will need to be examined when performing a binary search for a value in this data structure?

A) 5
B) 7
C) 8
D) 64

assuming i am understanding what the question is asking (i strongly dislike the phrasing) the “data structure” seems to be an array consisting of 128 integers (which you already knew), however the maximum index is actually 127 since the array is 0 indexed in JS and the maximum number in a 7 bit integer is 127 at least from my understanding