Read the given extract and answer the question that follow:

In some countries, power usually changes between two main parties. Several other parties may exist, contest elections and win a few seats in the National legislatures, But only the two main parties have a serious chance of winning a majority of seats to form government. Such a party system is called a two- party system. The United States of America and the United Kingdom are examples of a two-party system. If several parties compete for power, and more than two parties have a reasonable chance of coming to power either on their own strength or in alliance with others, we call it a multi party system. Thus, in India, we have a multi party system. In this system, the government is formed by various parties coming together in a coalition. When several parties in a multi-party system join for the purpose of contesting elections and winning power, it is called an alliance or a front. For example, in India there were three such major alliances in 2004 parliamentary elections~ the National Democratic Alliance, the United Progressive Alliance and the Left Front. The multi- party system often appears very messy and leads to political instability. At the same time, this system allows a variety of interests and opinions to enjoy political representation.

Which party leads the ruling NDA government at the Centre?