What are these two talking about

A．She knows Professor Arnold has come.
B．She thinks Professor Arnold has checked in.
C．She is sure that Professor Arnold has arrived.
D．She doesn’t know whether Professor Arnold has arrived.

A．Distinguished professors at research universities should concentrate on research only.
B．The separation of teaching from research can lower the quality of future scientists.
C．It is of utmost importance to improve teaching in elementary schools in order to train new scientists.
D．The rapid development of modern science makes it impossible to combine teaching with research.