1.spending
2.doing
3.learning
4opening
5.lending
6.collect

1. I hope my sister will enjoy ..spending...... time with her cats ( spend)
2. Do you enjoy .......doing... DIY in your free time? ( do)
3. My daughter loves ....learning... foreign languages. ( learn)
4. Do you mind ......opening.... the windown? ( open) 
5. If I were you, I wouldn't mind ..lending..... Bill this book.( lend)
6. We need ....collecting.... ten stamps before we can get the free glass of juice.( collect)