The correct answer is - C. gave Japan a foothold on the Asian mainland.
With the win of Japan over Russia in the Russo-Japanese War of 1904-1905, Japan managed to gain territory on the Asian mainland, thus marking the beginnings of its further expansion on mainland Asia.
Japan managed to gain the territories of Guandong and South Sakhalin in this war for dominance in the region. That was a stepping stone for the Japanese in the coming period to take over territory from China, mostly Manchuria, as well as the Korean Peninsula, as part of their mainland Asian territory.