1 .
What does
$$
\sum_{k=1}^{m} {m \choose k}
$$
count?
(a)
The number of bitstrings of length $m$ having exactly $k$ many 1s.
(b)
None of the above.
(c)
The number of non-empty subsets of a set of size $m$.
(d)
The number of subsets of a set of size $m$.