问题
选择题
Scientists ____ thousands of chemicals before they decided on the right one in the end.
A．tried out
B．found out
C．worked out
D．turned out
答案
答案：A
这题是词组辨析：try out试验 find out查明work out制定出、锻炼 turn out结果是，A符合句意：科学家试验了成千上万的药品才做出正确的决定。