My grandparents spend much time on their collections.=My grandparents spend much time ( collecting )things.
2.We both like collecting toys.= ( Both of ) us like collecting toys.
1. The dog ate its dinner ( it's-> its 它的,后接名词)
2. He showed her the dinner.( she-> her 动词后的代词要用宾格）
3The black one is his（ 没有错‘ 黑色的那只是它的’.
The white one is mine ( my-> mine 名词性物主代词）.
4. I asked him about the problem( his -> him ).
5.My room has bigger windows than hers.( her-> hers )
祝你假期愉快!加油!不明白再问!