大家好，这是在剑桥网络字典查到关于 turn 当 become 的意思的例句.. .
The weather has suddenly turned cold.
She turned pale and started to shiver.
The mood of the meeting turned solemn when the extent of the problem became kn own.
Keele, pop star turned business tycoon, has launched a new range of cosmetics.
为什么前面的句子turn都是主动表示，就独独在最后一句是被动呢？ 求解..