In this task, you are given a sentence. You must find the primary subject in the supplied sentence. The output must be a sub-sequence in the sentence.

Rot-proofing neither weakens the rope nor increases its weight, but makes it watertight to the extent that, when wet, it absorbs hardly any water and is nearly as light and as easily handled as when it is dry.
Rot-proofing

This should be secured in the stern-sheets of the first boat.
This

The rope will stretch under load, but may be expected to regain its normal length when slack, provided that the load applied is well within the breaking strength of the rope;

The rope