压力在7.0MPa以下温度在50°C以下，露天寒冷和严寒区使用（）液压油。
A、HR
B、HL
C、HV
D、HS
参考答案：A
Her mother ______ having read the letter.[ ]
A. thought
B. considered
C. admitted
D. advised
―When was the house built?
―It was built in 1949 _______ the PRC was founded．
A．which
B．that
C．what
D．when
