Find the missing term in the sequence: 35, 70, 140, 280, ___

Divide the second term by the first term:

$$70 \div 35 = 2$$

Divide the third term by the second term:

$$140 \div 70 = 2$$

Divide the fourth term by the third term:

$$280 \div 140 = 2$$

The pattern is that each term is multiplied by 2 to get the next term.

The last given term is 280. To find the next term, multiply 280 by 2.

$$280 \times 2 = 560$$

The missing term in the pattern is 560.

Comparing this with the given options:
A. 420
B. 560
C. 350
D. 400

The correct option is B.

The final answer is $\boxed{\text{560}}$.