he often thinks of 【how】he can do more for the four modernizations
he (主语）often（状语（ thinks of （谓语）【how】he can do more for the four modernizations（宾语从句）
i can't understand【why】they insist on going by motorbike
我不明白他们为什么坚持要骑摩托车去.
they insist on going by motorbike 这是个宾语从句.主谓宾齐备,显然从整个主从复合句来看,是缺一个副词why"为什么”,指“原因”
they （主语）insist on （谓语）going by motorbike （宾语）
------两个句子,我没看到哪个和定语从句有任何关系呀?!
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