Which formula CORRECTLY depicts the elongation in a composite body?

A

$$\delta = \frac{P}{E}\left[\frac{l_1}{A_1} + \frac{l_2}{A_2} + \frac{l_3}{A_3} + \frac{l_4}{A_4} + ...\right]$$

B

$$\delta = \frac{P}{AE}[l_1 + l_2 + l_3 + l_4 + ...]$$

C

$$\delta = \frac{P}{AE}[l_1 l_2 + l_3 - l_4 + ...]$$

D

$$\delta = \frac{Pl}{E}\left[\frac{1}{A_1} + \frac{1}{A_1} + \frac{1}{A_1} + \frac{1}{A_1} + ...\right]$$