1. C) that they're poor
Beans are one of the cheapest food in the world, although yummy and nutritive, people who are not poor are less likely to buy beans on a regular basis, unlike this old couple the author is describing, which eat beans mostly. In the poem, of course, eating beans is just one of the several characteristics from which we can infer that they are poor.
2. A)Part of what Brooks wants to communicate is the everyday nature of their very minimal existence.
Brook describes a simple scene: an old poor couple who are having dinner in their "rented back room", and their overall everyday actions and characteristics: they are "Mostly Good", they live their day, keep on putting on their clothes, keep on putting things away, and remembering (like old people normally do). At first sight, the characters are not interesting, exciting, something worth watching as they do normal things. However, the author's intention is to turn the reader's attention to the simple and everyday things and communicate the everyday nature of the couple's very minimal existence.
3) A) "Remembering, with twinklings and twinges,"
For many old people, remembering good times is one of the main sources of joy, it may affect their everyday life, even if it does not makes them excited as before. For the couple, these memories are strong enough in the present to give them “twinklings and twinges.".
4) The speaker of this poem is A) an observer, like a fly on the wall.
The poem is narrated from a third-person perspective, from an outside looker, as he or she uses pronouns like "They", and refers to them as "Two".