Whales and dolphins have been found with hind limbs; this rareoccurrence is due to the reemergence of a trait they inherited from their terrestrial ancestors.
发现鲸和海豚身上有后肢;这种稀有的现象是由于它们在陆地上的祖先身上的特征再次被遗传。
2
Experts state that the occurrenceof the high temperature this week is rather rare, though not unprecedented.
专家表示,本周所出现的高温现象虽然不是史无前例,但也相当罕见。
3
If the number of iterations is known and fixed — a rareoccurrence — that number appears in square brackets following the asterisk.