根据语篇情景，用恰当的短语或句子填空，使之意思完整。

Class Nine 1.________________________ on the school trip. They went to Blue Water Aquarium for the day. First they visited the Visitors’ Center and watched a movie about sharks. Then they watched a dolphin show. After that, they went to the Outdoor Pool and saw a big octopus. After lunch, they went to the Gift Shop and 2.____________________________. Finally, tired but happy, they took the bus back to school. At the end of the day, the science teacher 3. __________________ because the class monitor cleaned the bus after the trip.

怀特海说：科学研究的概率是999个想法会没有任何结果，可是，第1000个想法也许会改变世界。可见，好想法的产生不是________的。填入划横线部分最恰当的一项是（）。

A．随心所欲

B．轻而轻举

C．一蹶而就

D．信手拈来