Dear Siraaji:
In the first excerpt, I would use 5 1 2 1 4 1 4 1, with some wrist movement in the 4141.
In B, the questions are: how fast you have to play, and what articulation you want. I see no problems to play with a single finger if you want a "slow to moderate" and stacatto bass. Although you use one finger, you don't actually play with it: use your wrist or (if some strenght is required) your forearm. Anyway, I would use 4 3 2 1 to play this. It shall seem tricky, but once you get acquainted, it's very confortable and easy to do.
Third excerpt: what is your doubt? It's straightforward, but the sustained E. It have to be played with a thumb, either right or left. Try and figure out what is better to you. There's no difference in sounding.
Hope it helps! Best wishes!