Reason: Friends is a classic American drama, which shows the friendship, love and life between six friends in a humorous way. Its dialogue is simple and easy to understand, and its speech speed is slow, which is suitable for beginners.

2. Sherlock (English drama)

Reason: Sherlock is a classic English drama, which solves a series of suspense cases around Sherlock Holmes and Watson. Its dialogue is more complicated, but its speech speed is moderate, which is suitable for advanced learners.

3. Crown (English drama)

Reason: The Crown is a historical drama about the British royal family, which not only shows the life and court culture of the British royal family, but also involves political and historical knowledge. Its dialogue is more formal, but its speech speed is moderate, which is suitable for advanced learners.

4. The Big Bang Theory (American TV series)

Reason: The Big Bang Theory is a comedy featuring scientists, which shows the combination of scientific knowledge and life in a humorous way. Its dialogue is simple and easy to understand, and its speech speed is slow, which is suitable for beginners.

5. Downton Abbey (English drama)

Reason: Downton Abbey is a historical drama about British upper class, which shows the life and relationship between nobles and servants. Its dialogue is more formal, but its speech speed is moderate, which is suitable for advanced learners.