伸{の}びる versus 延{の}びる in a JLPT question


In my JLPT workbook, it gives these examples to explain the difference between
`延{の}びる` and `伸{の}びる`:

> 髪{かみ}は[１]{いっ}か[月]{げつ}に１センチぐらい伸{の}びる。
>
> 会議{かいぎ}はいつも30分{ぷん}ぐらい延{の}びる。

They both mean "stretch", more or less, so I assumed the difference was that
`延{の}びる` was more about time and space, and `伸{の}びる` is more about distance
and length.

However, take a look at this practise question:

> １９７２年、東京{とうきょう}から大阪{おおさか}までだった東海道{とうかいどう}新幹線{しんかんせん}は岡山{おかやま}まで____________。
>
> **A** 長引{ながひ}いた **B** 広{ひろ}がった **C** 延{の}びた **D** 伸{の}びた

I chose, **D** , because it was about length.

According to the book, though, the answer is **C**.

How can I make sense of this answer in light of the example sentences?




Using the Microsoft IME as a guide, generally 延びる seems to be used as "extend"
and 伸びる as "grow":

**延びる:**

  * Extend a conversation
  * Extend a schedule
  * Extend life span
  * Extend a subway into the suburbs

**伸びる:**

  * Plants/people grow
  * Expand investigations (in relation to the law etc)
  * Grow one's knowledge
  * Grow a market/earnings




Using the Microsoft IME as a guide, generally 延びる seems to be used as "extend"
and 伸びる as "grow":

**延びる:**

  * Extend a conversation
  * Extend a schedule
  * Extend life span
  * Extend a subway into the suburbs

**伸びる:**

  * Plants/people grow
  * Expand investigations (in relation to the law etc)
  * Grow one's knowledge
  * Grow a market/earnings

