单项选择题

The use of helium for deep-sea diving

A．helped to overcome the physical discomforts the divers experienced when nitrogen was used.
B．was found by Dr. Jeol Hiderbrand.
C．is still universally acknowledged as standard practice up to now.
D．all that is included in A, B, and C.

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单项选择题

What's the reason for Dr. Jeol Hiderbrand's interest in chemistry

A．His chemistry teacher was a great teacher.
B．His parents taught him chemistry when he was very young.
C．He was born in a time young people had greater freedom to decide what they wanted to do.
D．His talents were greater than his chemistry teacher.

单项选择题

The data accumulated was obtained through

A．observation by social psychologists.
B．conversations with mothers of the children.
C．interviews, school records and physician' reports.
D．observations of fathers with their children.