To a worker, ________ from the point of view of society is necessary labor is from his own point of view voluntary play.
A、whatA
本题要求填入一个关系代词引导主语从句，并在主语从句中作主语，所以选what。
名词解释：abilloflading
Sofarscientistshaveonlyacquired________understandingofthephysicalprocessesthatcauseearthquakes.
名词解释：preferredstock
Importswillbeallowedinproportion_______exports.
Thechallengeisnotoneofexpansion._______,therapidgrowthinenrollmentoverthelast40yearshascometoanend.
