Curiously enough这是副词,作状语.
动词开头,可以用原形、不定式、动名词、现在分词等.
Come to school on time.祈使句
Reading is important in learning a language.动名词
Seeing from the top of the hill,we can see the whole city clearly.现在分词
To see is to believe=Seeing is believing.不定式/动名词.副词开头是作什么状语呢？？副词开头是【强调该副词】，同时，也用来作状语，可以表示时间、地点、原因、方式、伴随、比较、让步等。这个句子中，Curiously enough表示【原因】，即做原因状语，表明【he opened the box...】的原因。