Whenever we see that the beginning of a sentence is set off with a comma, we should immediately start looking for modifier errors.

A modifier is a piece of descriptive information that describes what it is next to. A modifier at the beginning of the sentence, like this one, will always describe the noun it is closest to.

So here, we want "not unlike many birds' nests" to describe the noun closest to it.

A. Here, the sentence says that "birds' nests" are not unlike the "Musgum people of Cameroon". Comparing birds' nests to people doesn't make sense. Eliminate.
B. This sentence compares "birds' nests" to the "huts" of the Musgum people. This makes sense: we're comparing one home (nests) to another home (huts). Keep for now.
C. This compares "birds and their nests" to the "Musgum people of Cameroon". While we could compare "birds and their nests" to the "Musgum people of Cameroon and their huts", this doesn't make sense. Eliminate.
D. This compares "birds' nests" to "huts", like B. Keep for now.
E. This compares "birds' nests" to the "Musgum people". Eliminate.

To decide between B and D, we look at the difference between "just like" and "not unlike". "Just like" means that the two things being compared are *exactly* the same. However, we know that "constructed using few, if any, sophisticated tools" doesn't really apply to birds' nests - birds do not use sophisticated tools. A "hut" is not exactly the same as a birds' nest, so we want something a little more forgiving, that says the two things are similar in some ways. "Not unlike" gives us just that. D is the correct answer.