做新多益阅读大全时，时态的章节有特别提到:
现在进行式(be +Ving)的形式也是表现未来预定的事或是将要发生的事
请问如下练习题，为什么不能选(A)呢？
选现在进行式？
Mr. Sanders __(B)___ out of the country until next Friday, but you can contact him by e-mail if there are matters of urgency.
(A) is being
(B) will be
(C) will have been
(D) has been
谢谢！