How To Solve UKLO Mandombe Problem

Question

Premise

I was looking at a two-part problem from the 2021 UKLO titled "Mandombe". UKLO is a linguistics olympiad, which is mostly a code-breaking competition. In this problem, we were given a list of words in the Mandombe script and their corresponding transliterations in the Latin alphabet. Mandombe is a script used to write several languages of the Democratic Republic of the Congo.

For reference, I included both problems

The Problems

This first problem requires you to match the letters to the numbers.

This is the second question.

My Question

I figured out part 1), and checked it with the answer key. It is right. The key is below

However, I am confused how to do part 2)

My Progress

Based on the answers for part 1), I doubted that choices a), c) and d) were correct. For part 1), when there were two line segments, there was also a character with a single line segment. But I couldn't figure out how to eliminate b) or e).

The Answer

According to the answer key, the answer is e).

My Question

How would you figure out 2)?

Thank you for your time

Answer 1

The numbers 1 through 5 are based on the five basic vowels in Mandombe: i, u, e, o, and a.

You can find the "closed triangle" shape of the number 4 in any syllables that contain an o vowel, like both syllables of Q (mongo) or the first syllable of I (ngombe). And similarly, you can find the "open triangle" or "Z" shape of the number 5 in any syllables that contain an a vowel, like both syllables of R (maza). (Similarly the single stroke for i, the double stroke for u, and the "fork" for e.)