They________extensiveandpossiblydangerousactualflighttraining.
B
句意：他们经历了大量的并且可能是危险的实际飞行训练。
They________extensiveandpossiblydangerousactualflighttraining.
Thisisthefirsttimethatawomanhasbeen________tothepost.
Generallywecoverinsuranee__definite(明确的)instructionsfromourclients.()
Evenwiththenewdevelopmentinresearch,onlyatiny________ofalltestsaredonewithoutusinganimals.