コンクリート、モルタル、その他セメント系材料、陶・磁器タイル、石材、エポキシ樹脂系塗床材、English clauses which aren't imperatives must have a subject. Occasionally we have to use a ‘dummy’ or ‘empty’ or ‘artificial’ topic when there is no topic hooked up to the verb, and exactly where the re