Achieving a high degree of proficiency(精通）in English as a foreign language is   not a mysterious _______ without scientific basis.

The witnesses ______ by the police just now gave very different descriptions of the fight.

All their attempts to rescue the child from the burning building were _____, and he died soon.

Two years ago, she bought an expensive mountain bike and then she persuaded me to buy _______.

She has tried her best. Please don’t be too ______ about her job.

No matter how much time you spend planning a trip, things still _____ go wrong and air travel is no exception—from weather delays to lost luggage.

He pretended not to care but that remark     his real opinion on the matter.

We used to mistake that heavy objects fell faster than light       .

(2013·河南十校三次联考)She wanted to tell him that she didn't want to do that, but she didn't know how to ________ it.

Camels have three eyelids to ________ themselves from the blowing sand.