I had a strong desire to reach in and play with the toy, but ________ thankfully by the shop window.
A：am held back
B：held back
C：hold back
D：was held back
He is kind to me. He always ____ ____ ____ me with the problems in my study.
4位同学各自在周六、周日两天中任选一天参加公益活动，则周六、周日都有同学参加公益活动的概率为（ ）
