prep12 SC09

turbidtear

Roughly twice each century the planet Venus passes between the Earth and the Sun, an occasion known as a transit of Venus, during which it makes the outline of the planet  visible in stark relief.

B.during which the outline of the planet becomes
答案是上面这个，我想问duiring which前面要有表示一段时间的先行词吧？还是说根据句意是一段时间，就可以用？

谢谢！

tanklance

transit就是你说的那个“表示一段时间的先行词”