Our galaxy, being about 5 billion years old, has existed for roughly half as long as our solar system, which is estimated at 10 billion.
ans: about 5 billion years old, has existed roughly half as long as our solar system, estimated to be 10 billion year old
我不太懂為何這裡不需要加has-->as long as "has" our solar system
之前有討論過這本書Q149
http://www.formosamba.com/phpBB3/viewtopic.php?t=1464
這2者有什麼不同ㄋ???
麻煩各位幫我看看了
謝謝!!