Compared with grass,artificial turf requires more technical skills.
A、unreal 
B、realistic
C、artistic
D、natural

不定项选择纳米HAP的抗肿瘤活性与其浓度、粒径大小无关。

单项选择题Naples, in southern Italy, is known for its active, colorful community, as well as for its cultural and historic institutions.（ ）