A. 用方框中所给单词的适当形式填空。每词限用一次。

cost  during  success  enjoy  they

A company in the USA is there to help these dolphins. The scientists in this company solve this problem very . They have made robot dolphins. The robot dolphins not only look like real ones but also move like real ones. a test a week ago, people thought they were real dolphins. "The robot dolphins can swim and dive by , people can also see something when they watch them. " A worker in the company said.

One robot dolphin  about $27 million. Now, an aquarium in China is thinking about using them instead of real dolphins.