A:However hard may you try
B:Try however hard you may
C:However hard you may try
D:Try hard however you may
酸和碱的反应在工农业生产和日常生活中有广泛的用途.下列应用一定与酸和碱的反应原理无关的是( )
若命题“存在x∈R,ax2+4x+a≤0”为假命题,则实数a的取值范围是____ .