The only mistake is B6: "bird watching", not "birds watching". Although all the sentences are grammatical, some pairs have different meanings (for example, A8 & B8 are quite different).

A1: I thought of my school life when I saw this picture. = I saw this picture. It made me think of my school life. B1: I was thinking of my school life when I saw this picture. = I was thinking of my school life. Then I saw this picture. A2:He is an honest child and never tells lies. BASICALLY THE SAME B2:He is an honest child and never lies. A3: The birds are flying in a clear sky. SAME B3: The birds are flying in a sunny sky. A4: Putting together a piece of furniture is not an easy thing. ASSEMBLING B4: Setting up a piece of furniture is not an easy thing. PUTTING INTO AN UPRIGHT POSITION. A5: Most birds are active in the daytime. SAME B5: Most birds are active during the daytime. A6: We not only watched birds but also took part in some activities to protect birds. MOSTLY THE SAME - BUT ATTEND AND TAKE PART ARE NOT QUITE THE SAME. B6: We not only went bird watching but also attended some activities to protect birds. A7: People were trying to clear the snow from the street. B7: People were trying hard to clear off the snow on the street. MAYBE NOT WRONG, BUT KIND OF WIERD A8: People ran out in fear,but most of them were hurt by pieces of falling glass. FALLING = COMING DOWN FROM ABOVE. B8: People ran outside with fear,but most of them were hurt by fallen broken glass. FALLEN = ON THE GROUND, i.e. THE GLASS HAS ALREADY FALLEN BEFORE PEOPLE CAME OUT. A9: A moment of fear went through her mind and she shouted for help. MOMENT OF FEAR sound a little odd, but maybe it's just me. B9: A gust of fear swept her mind and she shouted for help.