Please, help me fill the gaps (I've got about ten exercises like these but I cannot answer only to these two).

[1] An original is a real-valued function of one real variable that satisfy the following conditions:
1) for all t<0, f(t) = 0,
2) in any finite interval (a,b) the function has a finite number of discontinuities of the ............ type
3) ...........

[2] A real-valued function of two real variables (z=f(x,y)) is called differentiable at the point (x_0, y_0) if its increment delta z = f(x,y)-f(x_0,y_0) may be written in the form
delta z = ..........., where epsilon_1 and epsilon_2 are function of variables ........ such that ........

Thank you very much in advance!