**Core Concept**
Millennium Development Goal (MDG) 5 aims to improve maternal health by reducing maternal mortality ratio (MMR). This goal focuses on ensuring universal access to reproductive health services, including family planning and emergency obstetric care.

**Why the Correct Answer is Right**
The correct answer is that MDG 5 aims to reduce MMR by 75% between 1990 and 2015. This reduction is a key target of the MDG 5, which aims to improve maternal health outcomes. The reduction in MMR is a crucial indicator of the effectiveness of healthcare systems in providing quality maternal care.

**Why Each Wrong Option is Incorrect**
**Option A:** MDG 5 does not aim to reduce MMR by 50%.
MDG 5 aims to reduce MMR by 75%, not 50%. This option is incorrect because it does not accurately reflect the target of MDG 5.

**Option B:** MDG 5 does not aim to reduce MMR by 90%.
MDG 5 aims to reduce MMR by 75%, not 90%. This option is incorrect because it overstates the target of MDG 5.

**Option C:** MDG 5 does not aim to reduce MMR by 67%.
MDG 5 aims to reduce MMR by 75%, not 67%. This option is incorrect because it does not accurately reflect the target of MDG 5.

**Clinical Pearl / High-Yield Fact**
MDG 5 has been replaced by SDG 3, which aims to end all forms of preventable deaths, including those related to pregnancy and childbirth, by 2030.

**Correct Answer:** D. 75%