Most types of synesthesia involve:
a sound
b. smells
c. tastes
d. colors

In the Manchurian Incident, the Japanese army acted on its own to overrun the whole of Manchuria. The correct option in regards to all the options given in the question is option "a". The invasion of Manchuria by the Japanese army began on the 18th of September in the year 1931. It was the Kwangtung army of the Japanese Empire that invaded Manchuria just after the Mukden incident. The Japanese Empire was successful in creating a puppet state by the name of Manchukuo and their occupation continued till World War II ended.