What character should replace the question mark in the sequence 3, 6, 9, ?, 15?

A. 12

What letter comes next in the series: A, C, E, G, ?

A. I

What is the code for the word 'HELLO' if H=8, E=5, L=12, O=15?

A. 8-5-12-12-15

What letter should replace the question mark in the series: A, E, I, M, ?

A. O

Teacher is to School as Doctor is to ?

A. HOSPITAL