spaces（回答）
UG先生からのご指名にお答えいたします。(spaces - 田邉祐司ゼミ 常時英心：言葉の森から)
spaceは不可算名詞ですが、その「空間」をある一定の目的ごとに分けると可算名詞にもなりうるというイメージを持ちました。やはり、LDOCEには”[uncountable and countable] an area, especially one used for a particular purpose”と載っています。
つまり、どれも陰惨な「殺人現場」ということではないでしょうか。それを婉曲的にspacesという書き方をしていると推測しました。あと、余談ですが印刷物やワープロなどで使う文字と文字の間隔に使うspaceもcountableですね。(Minnesota)
Varied Paths Toward Healing for Sites of Terrorized Schools
At Columbine High School, a glass atrium glistens in the sunlight.
A one-room schoolhouse in Nickel Mines, Pa., was demolished just over a week after the 2006 shooting of 10 girls inside.
Inside Virginia Tech’s Norris Hall, pastel walls enclose a peace center.
At Dunblane Primary School in Scotland, a flower garden welcomes students.
These spaces were once other things: the second-floor library where two killers completed a rampage that left 12 fellow high school students and a teacher dead; the classrooms where 30 college students and faculty members were gunned down by another student; and the gymnasium where 16 5- and 6-year-old children and their teacher were fatally shot by an intruder.
