(1)  Loom large = If something looms large it becomes very important and often causes worry.

• The thought of a third world war looms large in the minds of the humanity.
• Fear of failure loomed large in his mind.

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(2)  won’t budge an inch = will not move, change or shift in any way at all.

• Once my brother gets his mind made up, he won’t budge an inch.  So don’t bother trying to reason with him.
• I can’t believe how tight this bolt is on here, it won’t budge an inch.

. (3)  An unknown quantity = A person or a thing whose abilities, powers or effects are not yet known.

• We are still revising our new product, so its potential success is an unknown quantity.
• He is an unknown quantity for his rivals.