Find the false statement:
a. Linear polymers are typically more ductile than cross-linked polymers at the cost of less strength
b. Higher strain rate often makes the polymer more brittle
c. Relaxation modulus is a representative of stress drop with respect to the initial stress
d. An elastomer have some cross-linking but not as the thermosets

Option (c) is the correct answer.

Explanation:

Due to the structure of linear polymers they are highly ductile in nature. And, more is the number of strains present in a polymer more will be its brittleness.

Time dependent stress with respect to some strain level measure remains constant is known as relaxation modulus.

Mathematically,  

More cross-linking is present in thermosets whereas there is low degree of cross-linking in elastomers. Therefore, it means that an elastomer will have some amount of cross-linking but not as thermosets.

Thus, we can conclude that the statement relaxation modulus is a representative of stress drop with respect to the initial stress, is false.

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue

c) up is the direction the magnetic force is acting on the charge.