下列各有机物,在一定条件下自身分子间能发生缩聚反应,而在适宜的条件下分子内又能形成环状结构的是( )
All the dishes in this menu, ______ otherwise stated, will serve two to three people.
The children loved their day trip, and they enjoyed the horse ride ______.
Progress______ so far very good and we are sure that the work will be finished on time.
Charles was alone at home, with_______ looking after him.
It is often ______ that human beings are naturally equipped to speak.