I am not quite sure- but thought" mna meli kubwa " ought to be accepted too...didn't report because ...
Mna refers to something that is 'inside' something else. An example in this course is Mna matunda kikapuni: there is fruit in the basket. To put a big ship inside something else might be difficult :)
Det var så lite så! :)
Coukd you say: mna meli baharini?
Why is Pana meli kubwa in correct?