His comprehensive surveys have provided the most__________statements of how, and on whatbasis, data are collected.
A. explicit B. ambiguous
C. original D. arbitrary
Generally，students' inner motivation with high expectations from others ________ essential to their development.
A．is B．are
C．was D．were
The university estimates that living expenses for international students ________ around $8，450 a year, which ________ a burden for some of them.
A. are；is B. are；are
C. is；are D. is；is
In our class, when the bell rang and the teacher closed his book, it was a ______ for everyone to stand up.
A. signal B. chance
C. mark D. measure
Carbon dioxide, which makes a ________ between us and the sun, prevents heat from getting out of the atmosphere easily, so the earth is becoming warmer.
A．difference B．comparison
C．connection D．barrier
With inspiration from other food cultures, American food culture can take a ________ for the better.
A．share B．chance
C．turn D．lead
