What did the people of Border Cave and other OLD STONE AGE people use for shelter?

Explanation:

The period between ca. 40,000 and 20,000 y ago in South Africa is poorly known, and the timing of the Middle Stone Age (MSA) to Late Stone Age (LSA) transition is debated. In 1999 the LSA was defined (1) as a culture-stratigraphic unit that includes all assemblages dated within the last 20,000 y, characterized by artifacts such as hafted microlithic tools; bored stones used as digging-stick weights; bows and arrows; polished bone tools, such as awls, linkshafts, and arrowheads; fishing equipment; beads of shell and ostrich eggshell; and engraved decoration on bone and wood items.

The earliest technological expression of the LSA would be the Robberg Industry dated ca. 22–21 to 12 ka BP (1–3).

In the 1970s Beaumont and colleagues described the Border Cave stratigraphic sequence (SI Appendix, The Site) ranging from ca. 200 ka to the present (4–8). In the upper part of the sequence two layers, 1WA and 1BS Lower B+C, now dated 44–42 ka cal BP, contain evidence of some remarkable changes in stone and organic tool manufacture and in the making of decorated objects and personal ornaments. Some of these innovations have antecedents in the preceding Howiesons Poort (HP) and Still Bay periods (1), but they disappear or are extremely scarce in the following post-HP period, ca. 60–40 ka (9). According to Beaumont, the appearance of new tools and ornaments [bored stones, digging sticks, ostrich eggshell (OES) beads, bone points, engraved bone, and wood objects], together with high frequencies of microliths made by the bipolar technique and hafted with pitch, and of scaled pieces mark the beginning of the LSA (early LSA or ELSA) at Border Cave.

Some scholars have accepted this interpretation (10); others have rejected it (11), expressed doubts about the association of organic artifacts (11–13), or suggested that the transition MSA–LSA took place between 32 and 22 ka, setting the beginning of the LSA at 22 ka (14, 15). The temporal boundary between the MSA and the LSA and how the transition took place in the region remain controversial. New data are warranted.

the answer is either c or d i think its d