alone修饰的多为代表具体事物的名词,强调“个体 单独”之意
these指代名词,译作“仅仅这些”便顺理成章了
如果要强调时间,可以将alone换作only 或者 just
而且句式一般会发生变化,for example
Building these(buildings) just took sixteenth months.
Or
It just took sixteenth months to build these(buildings).