I saw him in the library yesterday. He ________ a book at that moment.
A:reads
B:is reading
C:was reading
D:will read
19世纪晚期,推动石油开采业发展和石油化工业产生的直接原因是
影响生物生活的因素有两类:____因素和____因素,前者如____、____、____、____、后者包括____、____、____.