单项选择题
A．the operator B．an emergency number C．a practice number for children D．used to keep children calm
A．$ 5,000. B．$ 5,000. C．$ 10,800. D．$ 15,800.
A．to make some sounding experiments in the oceans B．to collect samples of sea plants and animals C．to estimate the length of cable that was needed D．to measure the depths of the two oceans