With her bad eyes, Erin could not recognize Katrina , so 
OPTIONS:
- Erin had to ask her who she was.
- Katrina had to ask her who she was.
Erin had to ask her who she was.

He wanted to buy a digital or acoustic piano for his new home and he chose the 
OPTIONS:
- Digital piano because it was cheaper.
- Acoustic piano because it was cheaper.
Digital piano because it was cheaper.

She had a lower back pain but her headache was gone, so the 
OPTIONS:
- lower back problem was bothering her.
- headache problem was bothering her.
lower back problem was bothering her.