Bond - Fourth papers

[JaneEyre]

I am afraid, I am stuck on the question 8 page 52 of the New edition (i.e. question 8 page 53 in the old edition).
This is the question with the 'strands of threads' or 'pen stroke' as you prefer...
I know that the answer needs 6 'strands' so answers c and d are out.
e has a very different pattern so is out too. (though my thinking is may be not rational enough or precise enough. May be you have a better explanation to cross this one out?)
But how can we chose between answer a and b?

Thanks in advance for your help!

[KS10]

Is it the number of intersections? It increases by one each time (=a).

[fm]

As Ks10 says, it is intersections and not number of lines.

[JaneEyre]

Awwww! Thank you so much! It's crystal clear.
I am really thankful for this forum and everybody who takes time to answer questions!