推論題
Paragraph 1：When the Sun first formed 4.6 billion years ago, it was about 30 percent less luminous than it is today.
The Sun's luminosity increased slowly at first and then more rapidly as the buildup of helium in its core continued.
At present, the Sun is thought to be brightening by about one percent every hundred million years.
By the time the Sun ends its lifetime as a normal star, about five billion years from now, it is expected to have brightened by a factor of two to three as compared to today.
1. Which of the following can be inferred from paragraph 1 about the early Sun？
O It contained less helium than it does today.
O It was larger in size than it is today.
O Its luminosity increased more rapidly than it does today.
O It was brighter than it will be near the end of its lifetime.
A. It contained less helium than it does today. 正確
文中提到「as the buildup of helium in its core continued」＝隨著氦的累積，亮度逐漸上升。
這隱含太陽核心裡的氦含量在早期一定比現在少，否則不會有「持續累積」。
所以這是唯一能從段落中合理推論出的選項。
B. It was larger in size than it is today. 錯誤
段落完全沒有提到太陽大小（半徑或體積）的比較。
太陽演化中確實會變大（紅巨星時），但這是外部知識，非段落所提供的推論。
因此不能根據本文得出此結論。
C. Its luminosity increased more rapidly than it does today. 錯誤
段落說明「increased slowly at first and then more rapidly」= 早期太陽亮度增加速度很慢，後
期才加快。
現在的速率是「每一億年增加約1%」，這比早期更快。
所以早期的增加速度 更慢，不是「更快」。
D. It was brighter than it will be near the end of its lifetime. 錯誤
段落明確說到：「By the time the Sun ends its lifetime… it is expected to have brightened by a
factor of two to three as compared to today.」
這表示未來太陽會比現在 更耀眼 2–3 倍，而早期比現在暗 30%。
所以早期的太陽絕對沒有比後期更要耀眼。