D
本句的意思是：“即使研究有了新的发展，只有一小部分的试验可以不用动物”。因此答案为D。variety和plenty分别表示“多样”和“大量的”，意思不合适。amount后只能接不可数名词，而test是可数名词。
Somelinguiststhoughtthatalllanguages______andwereruledbyacommongrammar.
Wecannot_____presententertainanyfreshordersforYoungerBrandMen'sShirts.()
Before the 16th century, Latin was taught and learned for____________.
He has deep love for the people and ________ loyalty to the country.
The theory of language underlying the Grammar-Translation Method was derived from _____ Linguistics.