What has he been doing _________? I haven’t seen him much recently.

They’re ______ choosing a cautious policy in order to avoid a risk in such an important event.

Mrs Black isn’t in and I’ll have to ring ______. I would appreciate it if you ring _____ after 6 o'clock?  

--- Tomorrow we’ll go hiking in the mountain to experience nature.---- ___ it rains heavily when we are still halfway?

Medicine depends on other fields for basic information, particularly some of their specialized branches.