D. ABC, in which EFG holds a 10% voting equity interest, while PQR holds a 70% voting equity interest in ABC.

According to International Accounting Standard (IAS) 28, an associate is an entity over which the investor has significant influence, typically defined as having a voting equity interest of 20% to 50%. In situation D, EFG holds a 10% voting equity interest, which, while not meeting the typical threshold for significant influence, may still be considered an associate if EFG has the ability to significantly influence the operating and financial policies of ABC due to the large holding by PQR (70%). The combination of EFG's holding and the potential influence that comes with PQR's majority ownership could lead to EFG having significant influence over ABC.

In situation A, the 12% voting equity interest and the low level of transactions between EFG and STU do not indicate significant influence. Situation B does not classify LMN as an associate because EFG lacks representation on the board and necessary financial information. In situation C, while there is a close relationship due to shared management, the 15% voting equity interest alone is not enough to classify XYZ as an associate under IAS 28 without additional evidence of significant influence.