申报历史文化名城的，在所申报的历史文化名城保护范围内还应当有（）个以上的历史文化街区。

A.1

B.2

C.3

D.4

Research on animal intelligence always makes me wonder just how smart humans are. (51) the fruit-fly experiments described in Carl Zimmer’s piece in the Science Times on Tuesday. Fruit flies who were taught to be smarter than the average fruit fly (52) to live shorter lives. This suggests that (53) bulbs burn longer, that there is an advantage in not being too terrifically bright.

Intelligence, it (54) , is a high-priced option. It takes more upkeep, burns more fuel and is slow off the starting line because it depends on learning—a (55) process—instead of instinct. Plenty of other species are able to learn, and one of the things they’ve apparently learned is when to (56) .

Is there an adaptive value to (57) intelligence That’s the question behind this new research. I like it. Instead of casting a wistful glance (58) at all the species we’ve left in the dust I.Q.-wise, it implicitly asks what the real (59) of our own intelligence might be. This is on the mind of every animal I’ve ever met.

Research on animal intelligence also makes me wonder what experiments animals would (60) on humans if they had the chance.

57().

A.invisible 

B.limited 

C.indefinite 

D.different