Are these his shoes? No, they____ (aren't/are).
鸟卵即可贮存丰富的____供胚胎发育需要;又有卵壳、卵壳膜的保护,能减少____的丢失.
下列物态变化中,属于凝固现象的是( )
儿童青少年心理健康的核心是( )