答案：C

考查从句。_____ makes a new invention such a wonderful thing是主语从句，且从句缺少主语，用what引导，排除B,D; ____ it allows us to do something是表语从句，且不缺成分，所以用that引导；something是不定代词作先行词，在定从____ we could not do before中作do的宾语，用that引导，也可省略。所以选C。