In writing up the answers to these, I've tried to use slightly different syntax each time. It is essentially one of the same two messages over and over, but expressed in slightly different manners.
Remember: if you find a minimal pair, the two sounds contrast and are different phonemes: English dime/time. You can substitute a /d/ for a /t/ and get a new word. /d/ and /t/ can occur in the same environment: the same place in a word.
If you find a pattern for the occurrence of the two sounds, they are in complementary distribution and are allophones of the same phoneme: For example, English t and aspirated t are in complementary distribution: you cannot substitute one for the other. If you do substitute one for the other, you will never get a new word: just a badly pronounced version of the same word you started with.
Here are five sample problems.
1. [trok] building
2. [tagali] forest
3. [katamba] problem
4. [gelaza] wink
5. [gazalu] log
6. [zozok] office
7. [gatamba] reason
8. [kilio] smile