Extended cyclical variations in tensions will cause an anchor chain to break due to（）.

A.wooden blocks or dunnage placed between a deck load and the deck
B.the chains and shackles used to secure a deck cargo
C.a crate in which a deck cargo is packaged
D.cardboard separation pieces placed between deck loads to prevent chafing

A.has less strength than manila line
B.has more strength than manila line
C.is equivalent to manila line
D.will rot quicker than manila line

A.anchor the boat
B.pick up heavy loads
C.protect fiber rope from abrasion
D.strengthen mooring lines