**Core Concept**
Testicular tumors can be broadly classified into two categories: germ cell tumors and sex cord-stromal tumors. Germ cell tumors arise from the germ cells, which give rise to sperm, while sex cord-stromal tumors originate from the supporting cells surrounding the germ cells. Sex cord-stromal tumors can produce hormones, leading to various clinical manifestations.

**Why the Correct Answer is Right**
Sertoli cell tumors, a type of sex cord-stromal tumor, can produce estrogen in males, leading to feminizing symptoms. This is due to the tumor cells' ability to produce aromatase, an enzyme responsible for the conversion of androgens to estrogens. The excess estrogen production can cause a range of symptoms, including gynecomastia, testicular atrophy, and infertility. In addition, patients may experience a decrease in libido and an increase in breast tenderness.

**Why Each Wrong Option is Incorrect**
**Option A:** Seminoma, a type of germ cell tumor, is the most common testicular cancer, but it does not typically produce feminizing symptoms. Seminomas are usually treated with radiotherapy or chemotherapy, and they do not have a significant hormone-producing component.
**Option B:** Teratoma, another type of germ cell tumor, can contain various tissues, including hair, muscle, and bone, but it is not typically associated with feminizing symptoms. Teratomas can produce hormones, but this is not a characteristic feature of this tumor type.
**Option C:** Leydig cell tumors, a type of sex cord-stromal tumor, can produce androgens, leading to virilizing symptoms, such as acne, hirsutism, and male pattern baldness, rather than feminizing symptoms.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that sex cord-stromal tumors can produce hormones, leading to various clinical manifestations, and that Sertoli cell tumors are specifically associated with feminizing symptoms in males.

**✓ Correct Answer: D. Sertoli cell tumour**