be known to have done sth的问题：当be known 和 do sth的发生的时间一致时，用be known to do sth；而do sth发生在be known之前时，则要用be known to have done sth。 这个解释我觉得好理解点，约束力这种概念太模糊了
such effects could lead to several precursory phenomena in the field, including a change in the velocity of seismic waves, and an increase in small, nearby tremors.
adjective] ENOUGH to..." means, basically, "sufficient to meet a threshold/minimum requirement".
"SO [adjective] that...", on the other hand, is used to emphasize that something is EXTREME.
again, just make up examples in your head -- this time using "so big..." or "so tall..." or "so old..."
if your examples make sense, then, ALL of them will emphasize the EXTREME quality of whatever you are talking about.
adjective] ENOUGH to..." means, basically, "sufficient to meet a threshold/minimum requirement".
just think about typical examples of being "tall enough" or "old enough" or "good enough" for various things. these are NOT examples of "extremes"; they're just examples of "things that meet minimum requirements".
D的选项应该是这样的吧？
Leakey's contributions to archaeology include her discovery of the earliest direct evidence of hominid activity and her painstaking documentation of
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be known to have done sth的问题：当be known 和 do sth的发生的时间一致时，用be known to do sth；而do sth发生在be known之前时，则要用be known to have done sth。 这个解释我觉得好理解点，约束力这种概念太模糊了