1.himself是he的同位语.
如果先D,应该是 he invented the machine to produce the new products by himself
2.翻译为：我姐姐已经大了,而不能被阻止去结婚了.（意思就是我姐姐已经到了能结婚的年龄了.）
3.这个since是作“因为”讲.
since在这个用法时,侧重主句,从句表示显然的或已为人所知的理由,常译为“因为”、“既然”,语气比because稍弱,通常置于句首,表示一种含有勉强语气的原因.
例如：
Since he asks you,you”ll tell him why.
他既然问你,那就告诉他为什么吧.
Since many of the customers work during the day,Billy has to collect the money at night.
因为许多顾客白天上班,所以毕利只好晚上去收钱.