读图,回答下列问题。
—How many people were invited to the meeting?
—About six ________.
一字组多词
隐____ ____ ____
绩____ ____ ____
纪____ ____ ____
①卵母细胞的采集和培养 ②精子的采集和获能 ③受精 ④胚胎的早期培养
若向量AB→=(1,2),BC→=(3,4),则AC→=( )