1. They offered me a commission in their navy. I’ve been requested to accept immediately, and report to their naval base in Bremer haven tomorrow.

(1) commission

N-COUNT If a member of the armed forces receives a commission, he or she becomes an officer.

(2) naval base

A naval base (military port) is a military base, where warships and naval ships are deployed when they have no mission at sea or want to restock. Usually ships may also perform some minor repairs.

(3) haven

N-COUNT a sheltered port where ships can take on or discharge cargo.

2. To refuse them would be fatal for all of us. And joining them would be unthinkable.

(1) fatal

ADJ A fatal action has very undesirable effects.

(2) unthinkable

ADJ If you say that something is unthinkable, you are emphasizing that it cannot possibly be accepted or imagined as a possibility.

3. If not only strain my back, it breaks my heart when I think of a certain singing group that will not appear at the festival tonight.

(1) strain

V-T To strain something means to make it do more than it is able to do.