A：在 Approximately 15 minutes is (or are) allowed for questions and comments. (允許約 15 分鐘提問和發表意見) 這句中，fifteen minutes 應被視為一個時間的總量，而以單數的實體來看待之；換言之，這裡要使用單數動詞 is，正如 Fifteen minutes is not a very long time. (15 分鐘不是一段很長的時間) 一樣。
當主詞為「一段時間」、「一筆金錢」、「一段距離」、「一個重量」時，若形式為複數，但意義上為單數時，須用單數動詞。然而，若這些複數名詞不是表示「單一的觀念」，則必須接複數動詞。例如：
- Ten miles is too long a distance for her to walk. (走 10 英里對她來說太長了)
Five meters of cloth have been measured off. (五公尺的布已經量好剪下來了) - Three hundred dollars is too much to pay for that book. (花 300 元買那本書太貴了)
One hundred cents make a dollar. (一百分就是一美元) - Twenty days is too long a time for me. (20 天對我來說太久了)
Three years have passed since I graduated. (我畢業迄今已三年了)
－ 複數時間名詞若與 pass 和 go by 等動詞連用，一般都用複數動詞。 - Thirty pounds is too heavy for me to lift. (30 磅太重了，我提不起來)
Three hundred and one kilograms of heroin have been seized this year. (今年已破獲 301 公斤的海洛因)