Which among the following was/were feature(s) of 'Subsidiary Alliance', a system devised by the British in colonial India?

(a) It was devised by Lord Wellesley.

(b) A British army contingent was to be stationed in the territory of the ally.

(c) The ally could never get into agreements with any other rulers.

(d) The British were to protect the ally only from the internal threats to power.

Choose the correct option from the codes given below: