单选题

考虑以下代码： NSMutableString * s1 NSMutab...

Question

考虑以下代码：

NSMutableString * s1
NSMutableString * s2
s1 = [[[NSMutableString alloc] initWithString:@"Hello world!"] autorelease]
[[[[s1 retain] retain] retain] release]
s2 = [s1 copy]
[s1 release]

s1和s2的引用计数分别是多少？

A. s1为2，s2为1

B. s1为1，s2为1

C. s1为2，s2为2

D. s1为0，s2为2