Spring in Nanjing is very short .It is warm and sunny .People (人们) like to go to the parks on sunny days . It is very hot in summer in Nanjing .People do not like to play balls in the afternoon .They like to go swimming in summer . In autumn , it is cool and sunny. Many people like to come to Nanjing in autumn .In winter , it is cold in Nanjing .Boys and girls like to make snowmen and go skating . They have great fun in winter .

My mother __________ at the school gate now.

把重6N、密度为0.8×10³ kg/m³的实心物体投入水中．当物体静止时，物体处于____ 状态（填“漂浮”、“悬浮”或“沉在水底”），物体所受的浮力是____ N，物体排开的水重是____ N． （水的密度为1.0×10³ kg/m³）

下列对生物进化总体趋势的描述不正确的是（　　）