A：on, adds up to
B：with, adds u
C：about, added u
D：with, added up to
某班第一小组6名女生在测仰卧起坐时，记录下她们的成绩（单位：个/分）：45，48，46，50，50，49．这组数据的平均数是（ ）.
— Children today find it hard to focus on study.
— Exactly, as they ________ so many fun things to do.
—________.
