Nobody knew who was the first ________ at school that morning when the window was broken.
A:arriving
B:arrived
C:to arrive
D:have arrived
为探究声音的反射与吸收特点,小明同学进行了实验探究。
绿色植物通过光合作用维持了生物圈中二氧化碳和氧气的相对平衡 ( )