Last weekend we had a birthday for our classmate Zhang Xiaohui. She is younger than me, but I am shorter than her. And she looks stronger. Of course she is heavier than me. We went to a shop to buy a present for Xiaohui. What did we buy? We bought a doll for her. Because she told me " I haven't got a lovely doll." When she got our present she looked excited. She was very happy. We went to the zoo. We saw elephants. We wanted to row a boat in Jingming park, but it was later, we had to went home. We had a good time on that day.

人的性别是由性染色体控制的，男性的精子细胞中性染色体是（  ）

“良言一句三冬暖，恶语伤人六月寒”包含的道理是（）
①谦虚恭敬的言行举止是相互尊重、有效沟通的前提条件 ②傲慢粗鲁的言行会导致敌意、降低自身吸引力 ③与人交往是一门学问更是一门艺术 ④与人交往不要太直率，要学会虚情假意说好听的话 

为了保持天平测量精确，使用时不能超过____ ，并保持天平干燥、清洁.