LU Decomposition

Q. The matrix $\left[A\right]=\left[\begin{array}{cc}2& 1\\ 4& -1\end{array}\right]$ is decomposed into a product of a lower triangular matrix [L] and an upper triangular matrix[U]. The properly decomposed [L] and [U] matrices respectively are

1. $\left[\begin{array}{cc}1& 0\\ 4& -1\end{array}\right]$ and $\left[\begin{array}{cc}1& 1\\ 0& -2\end{array}\right]$
2. $\left[\begin{array}{cc}2& 0\\ 4& -1\end{array}\right]$ and $\left[\begin{array}{cc}1& 1\\ 0& 1\end{array}\right]$
3. $\left[\begin{array}{cc}1& 0\\ 4& 1\end{array}\right]$ and $\left[\begin{array}{cc}2& 1\\ 0& -1\end{array}\right]$
4. $\left[\begin{array}{cc}2& 0\\ 4& -3\end{array}\right]$ and $\left[\begin{array}{cc}1& 0.5\\ 0& 1\end{array}\right]$