题目内容：
根据以下内容回答题：It is Dredicted that there will be four scientific breakthroughs in the 21 st centruy．
We wiuknow where we came from．Since the l920s，scientists have known the universe is expanding，which means it must have started at a definite time in the past．They even have de-veloped theories that give a detailed picture of the universe from the time it was a fraction of a second old to the present．Over the next couple of decades，these theories will be improved by data from powerful new telescopes．
We will find out the genetic code and conquer cancer．In l9th century operas，when the heroine coughs in the first act，the audience knows'she will die of tuberculosis in the third act．But thanks to 20th century science，the once deadly disease now means nothing more serious than taking some pills．As scientists learn more about the genetic code and the way cells work，many serious desease--cancer．will become less threatening．
We will live longer，probably up to 1 20 years．If the normal aging process is basically a fierce．invisible contest in our ceus——a contest between damage to our DNA and our ceils’abili-ty to repair that damage，gre{at progress around．But before we push scientists to do more，we should consider：do we really want to live in a world where no one grows old?
We will haye a hrain road map．This is the real final frontier of the 21 st century．The brain is the most complex system we know．It contains about l00 billion nerve cells，each con-nected to as many as l000 0thers．Early in the 21 st century，progress in science will make it Dossible to produce detailed images of the nerve cells in operation．We will be able to say with certainty which ones are working when you read or think about a word．
Jadging from the second paragraph，the writer thinks of present theories about the uinverse as __________． A．perfect
B．imperfect
C．groundless
D．complicated
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