When Peter speaks in public, he always has trouble        _ the right things to say.

A．thinking of

B．to think of

C．thought of

D．think of .

下面有关DRAM和SRAM存储器芯片的叙述，正确的是( )。 Ⅰ DRAM比SRAM集成度高 Ⅱ DRAM比SRAM成本高 Ⅲ DRAM比SRAM速度快 Ⅳ DRAM需要刷新，SRAM不需要刷新

A．Ⅰ和Ⅱ

B．Ⅱ和Ⅲ

C．Ⅲ和Ⅳ

D．Ⅰ和Ⅳ