The capital of Australia is (A) Canberra. Canberra is the purpose-built capital city of Australia, chosen for its central location between Sydney and Melbourne. It officially became the capital in 1927, succeeding Melbourne. Canberra houses the key government institutions, including the Parliament House and the official residence of the Prime Minister.

Brisbane is not a former capital of Australia. The other cities are all former capitals of their respective countries: 

Karachi: The capital of Pakistan from 1947 to 1959

Auckland: A former capital of New Zealand

Kyoto: A former capital of Japan

Brisbane was the capital of Australia before Canberra from 1842 to 1859. 

London is situated on the bank of the (A) Thames River. The River Thames is a major waterway flowing through the city of London, and it has played a significant role in the historical and cultural development of the city. The Thames River is the longest river entirely in England and is central to the geography and life of London.

The steppe grassland is primarily found in (A) Asia. The Eurasian Steppe, also known as the Great Steppe, is a vast expanse of grassland that stretches from Eastern Europe to Siberia in Asia. It is one of the world's largest temperate grasslands and spans several countries, including Russia, Ukraine, Kazakhstan, and Mongolia.