A:①④
B:②③
C:①③
D:②④
He promised ________ his old friend during his stay in Tianjin
下面四幅图片所表示的科技成果,应用了转基因技术的是( )
引起传染病的病原体主要是细菌、病毒和寄生虫等。下列各种疾病中,由病毒引起的是 ( )
— __________.