There aren't any links included so I can't help you.
Looking at maps and the shapes of the lakes, I’d say it’s C, Lake Victoria, that 4 is pointing to
The answer is Octave a symbol used to notate a pitch and its
duration. Note is also used to identify a pitch or a tone. Octave is the
interval between one musical pitch and another with half or double its
frequency. It is defined by ANSI as the unit of frequency level when the base
of the logarithm is two.
The large ships launched people in the boats that are small and were launched so they are sboth shown