This pair of shoes __________ hand, and it __________ very comfortable.
A:is made with; is felt
B:are made from; is felt
C:are made of; feels
D:is made by; feels
_______ does Lucy like?
以虫治虫是生态农业的重要内容,右下图表示某一生态系统中四种生物所含有机物的总量。假设这四种生物只构成一条食物链,请问在一段时间内,如果甲的种群数量增加,其可能引起的后果是
下列命题:①至少有一个x使x2+2x+1=0成立;②对任意的x都有x2+2x+1=0成立;③对任意的x都有x2+2x+1=0不成立;④存在x使x2+2x+1=0成立.其中是全称命题的有( )