Which of the following statements about the compatibility equations are true:
P. Strain compatibility equations must be satisfied in the solution of three-dimensional problems in elasticity.
Q. Six strains are defined in terms of three displacement functions and can have arbitrary values.
R. Compatibility equations are an expression of the continuity of displacements.
(A) $\mathrm{P}$ and $\mathrm{Q}$
(B) $Q$ and $R$
(C) $\mathrm{P}$ and $\mathrm{R}$
(D) $\mathrm{P}, \mathrm{Q}$ and $\mathrm{R}$
Which of the following statements about the compatibility equations are true:
P. Strain compatibility equations must be satisfied in the solution of three-dimensional problems in elasticity.
Q. Six strains are defined in terms of three displacement functions and can have arbitrary values.
R. Compatibility equations are an expression of the continuity of displacements.
(A) $\mathrm{P}$ and $\mathrm{Q}$
(B) $Q$ and $R$
(C) $\mathrm{P}$ and $\mathrm{R}$
(D) $\mathrm{P}, \mathrm{Q}$ and $\mathrm{R}$