"Did you eat them?"
Can someone explain why it's mliVIla? It's the ki/vi noun class I pressume? How can you know? Ku from kula also dissapears?
Assuming the noun-class is one of the things that is frustrating in this course. It often seems to want the KI/VI class with no other context, but not always. Depending on the surrounding context, it should accept -i-, -ya-, -vi-, or -zi- (or if we're talking about animals or even people, then -wa-) ...
The reason why -ku- is missing is easier to explain. Whenever there's an object marker, the -ku- of monosyllabic verbs is dropped.
To go more in depth, the reason behind this is fairly complex to explain, but may help you understand where and why this -ku- appears and disappears.
There are certain parts of verbs that can't be stressed and when they would be the second last syllable, -ku- kind of jumps in front to take the bullet and save the day. I'll highlight the stressed syllable in these examples.
The positive tense markers -na-, -me-, -li- and -ta- (the latter both positive and negative) as well as some others like -nge-, -ngali-, -sha etc., can't be stressed, so to prevent them from being the second last syllable, this -ku- appears to take the stress. Eg. it's m-li-
ku-la "you ate" because ni-
li-la is not allowed.
The negative tense markers -ku- (for past), -ja- (for "not yet") can take stress, so they are not followed by -ku- (although some people sometimes use -ku- with these).
Subject and object markers can be stressed, so
m-le "you should eat" and m-li-
vi-la don't have the -ku-. Also, because in the negative present, there is no tense marker (well, more accurately, the negative present tense marker, -i-, appears at the end of the word), the subject prefix will take that stress. That's why m-na-
ku-la "you eat" becomes
The relative markers also cannot be stressed, so the -ku- appears in m-li-po-
ku-la "when/where you eat", but, of course, when there's an object, that appears in the place to take the stress, so the -ku- is dropped, as in m-li-po-
vi-la "when/where you ate them".