In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D".
Q: [header] How to insulate a basement [title] These concrete blocks are usually installed at the time of construction or when the home is undergoing significant renovation. [step] Unless you possess expert masonry skills, leave this kind of basement insulation to a cement mason. [title] Purchase concrete blocks infused with foam insulation. <sep> (A) [step] The two common forms sold are autoclaved aerated concrete (aac) and autoclaved cellular concrete (acc). [title] Most commonly, foam board is installed between an exterior finish such as siding and the exterior wall's studs. (B) [step] Their characteristics could vary widely by brand (having inside houses and apartments) or, of course, by your personal experiences with the wall. [title] Get concrete for the area where the inside houses it, and variously label the concrete blocks. (C) [step] In a conventional house, the available concrete costs 120 by 300 square feet. In a program like yours, the amount of available concrete is drastically reduced. (D) [step] These can be either pre-oiled concrete or heavy bricks. These materials can be purchased at masonry supply stores or at home improvement stores.
A:
A