英语定语从句练习的问题

英语定语从句练习的问题
第一道题是13.Meeting my uncle after all these years was an unforgettable moment,___B____ I will always treasure.
A.that B.one C.it D.what
1.the doctor,_____helped the engineer manage to invent a new instrument,was praised.
2.the doctor,_____help the engineer managed to invent a new instrument,was praised.
with whose 2.who
第一道题可以用排除法来答,但是想要一个比较合理的解释,
第二题两句中主要是后面从句help与manage的时态的不同,
要求解释清楚,不清楚不给分.
答案都是这样的了,无误,觉得第一题应该是这样解释的,那里要填的应该是one that 之所以选择了one应该是that省略了 ,