C. The activities during the picnic included ... 1) a boat race. 2) games and singing songs. 3) treasure hunt for adults. 4) swimming competitions.

Ответ:

• 2) games and singing songs.
• 3) treasure hunt for adults.

Пояснение:

В тексте сказано: «During the picnic they played many fun games like tug of war, sack races, and a treasure hunt... Mary's best friend brought a guitar and sang songs while they all sang along». Таким образом, среди активностей были игры и песни.