**Core Concept**
The question is based on the concept of **cosmic radiation exposure** at high altitudes, particularly during airline flights. At higher altitudes, the atmosphere provides less protection against **galactic cosmic rays** and **solar particle events**.

**Why the Correct Answer is Right**
The correct answer is based on the estimated exposure to **ionizing radiation** during a 5-hour flight at an altitude of 12 km. The exposure is typically in the range of 20-40 µSv for a 5-hour flight at such altitudes due to the decreased atmospheric shielding.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is too low for the estimated exposure.
**Option B:** This option is too high for the estimated exposure.
**Option D:** This option is significantly too high for the estimated exposure.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that **cosmic radiation exposure** increases with altitude and latitude, and airline crew members may receive significant cumulative doses over time.

**Correct Answer:** C. 10 µSv