In general______.is given to the students who pass examination at the end of 3 -4 years of study at the university in Britain.

A．Relied primarily on the data obtained from the analysis of Emiliani's core samples.
B．Combined data derived from the analysis of many different core samples.
C．Matched the data obtained by geologists with that provided by astronomers.
D．Evaluated the isotope-ratio data obtained in several areas in order to eliminate all but the most reliable dat

A．water molecules containing oxygen-18 condense and fall as precipitation slightly sooner
than those containing oxygen-16
B．the ratio of oxygen-18 to oxygen-16 in water vapor evaporated from oceans if different from that of these isotopes in seawater
C．growing ice sheets tend to lose their oxygen-18 as the temperature of the oceans near them gradually decreases
D．less water vapor evaporates from oceans during glacial periods and therefore less oxygen-18 is removed from the seawater