I didn't know she ____ play guitar when she was four 空里面是该填could还是can,为什么

I didn't know she ____ play guitar when she was four 空里面是该填could还是can,为什么
I didn't know she ____ play guitar when she was four 空里面是该填could还是can,为什么

I didn't know she ____ play guitar when she was four 空里面是该填could还是can,为什么
填could
"when she was four"是过去式,主要强调是她过去会弹.
这道题可以先把前面"i did not"删掉再看,对后面解题没影响."did not"容易考动词填空.

could 这是宾语从句 主句是I didn't know 过去时 从句除客观真理都用过去时

COULD
应该用过去时态，她四岁时，