9. Poems like "When You Are Old," written in long and feature an unstressed syllable followed by a stressed syllable. 10 syllables A. iambic pentameter B. trochaic tetrameter C. couplets D. ABAB form

Below is the step-by-step explanation: 1. **Identifying the Metric Pattern:** A line written in an unstressed syllable followed by a stressed syllable is called an *iamb*. This foot is represented as \(\text{iamb} = \text{(unstressed, stressed)}\). 2. **Counting Syllables:** The line is said to have 10 syllables. In poetry, if a line has 10 syllables divided into 5 metrical feet, it is known as *pentameter*. Since each foot here is an iamb, the line consists of 5 iambs. 3. **Combining the Terms:** - The term *"iambic"* refers to the use of the iamb as the metrical foot. - The term *"pentameter"* indicates that there are 5 such feet in the line. 4. **Conclusion:** Therefore, a poem like "When You Are Old" that features lines with an unstressed syllable followed by a stressed syllable and 10 syllables per line is written in \(\textbf{iambic pentameter}\). Thus, the correct answer is: **A. iambic pentameter**