這里whose修飾life,作life的定語(yǔ).引導(dǎo)定語(yǔ)從句的關(guān)系代詞中只有wose才可以作定語(yǔ).
題中whose life合起來(lái)作這個(gè)定語(yǔ)從句的主語(yǔ).
whose可以轉(zhuǎn)換成of which.這句話(huà)可以說(shuō)成：
He belives that earth is unlikely to be the only planetthe life of which has developed gradually.
或：
He belives that earth is unlikely to be the only planetof which the life has developed gradually.
或：
He belives that earth is unlikely to be the only planetwhich the life of has developed gradually.
人教版高中英語(yǔ)必修（二）附錄中好像有相似的例子.