**Core Concept**
Tubal block refers to the obstruction of the fallopian tubes, which can prevent fertilization and implantation of an egg. This condition is a significant contributor to female infertility.

**Why the Correct Answer is Right**
Tubal block is often caused by inflammation and scarring within the fallopian tubes, which can result from pelvic inflammatory disease (PID). The exact percentage of tubal block in tubal infertility cases can vary depending on the population and study. However, it is generally estimated that tubal block accounts for approximately 40-50% of cases of tubal infertility. This is because tubal damage can lead to a significant reduction in the chances of successful fertilization and implantation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the estimated percentage of tubal block in tubal infertility cases.
**Option B:** This option is incorrect because it may be too high, and there is limited evidence to support a significant percentage of tubal infertility cases being attributed to tubal block.
**Option C:** This option is incorrect because it is too low, and it is generally accepted that tubal block accounts for a significant percentage of tubal infertility cases.

**Clinical Pearl / High-Yield Fact**
It is essential to note that tubal block can often be diagnosed through hysterosalpingography (HSG), a type of imaging test that involves injecting a dye into the fallopian tubes to visualize their patency.

**Correct Answer: C. 40-50%**