GWD1-27关于 for several weeks是长期还是短期的问题

According to the passage, the periodic behavior displayed by commuter diatoms under constant laboratory conditions is characterized by which of the following?

相关的原文是: However, when diatoms are observed under constant conditions in a laboratory, they still display periodic behavior, continuing to burrow on schedule for several weeks.

A.   Greater unpredictability than the corresponding behavior under natural conditions

B.   A consistent periodic schedule in the short term

C.   No difference over the long term from the corresponding behavior under natural conditions

D.   Initial variability caused by the constant conditions of the laboratory

E.   Greater sensitivity to environmental factors than is the case under natural conditions

我觉得B和C的差别就是在对for several weeks 究竟是"short tterm“还是“long term“的判断？