99成大成99

[單選] which is correct?
(a) S={the 2x2 triangular matrix} is a subspace of R^2x2
(b) T={x| Ax=0 which A is nxn matrix} is a subspace of R^n
請問這題是長這樣嗎?! 又哪個是正確的? 謝謝