数えられない名詞（不加算名詞）とは何ですか？
回答
時間・金額・距離・重量を表す語が主語の場合、基本的に、形は複数形であっても単数扱いとなります。例えば：
◆ まとまって1つの単位とみなされる場合は単数扱いになります。
e.g., Forty miles is a good distance.
◆ 時の経過の場合、years, months, days, hours などは、複数扱いになります。
e.g., Five years have passed since he left home.
◆ 実際に支払われる金額や経過年数の数量そのものに関心がある場合には、動詞は複数形を用いることがあります。（ロイヤル英文法、その他より）
e.g., Three dollars were paid for the old coin.
e.g., The first five years are the hardest.
e.g., If you have German measles, ten days are necessary to recover.
結論： 基本的に単数扱いであるが、実際には話者の関心や文脈に依存している。
e.g., CNN
“Beyond three days, there are some suggestions that it could make a turn and head north. But three days are a long time in the weather world,” Blake said.
e.g., Memorial University, Canada
Recently our Department has celebrated its 25th year of existence. Twenty-five years are a long time in computer technology. In just these 25 years, the power of computers has increased 100,000-fold. Computer technology, software and hardware, has now invaded nearly all areas of human activity.