SC doubt about verb tense

[reachdeepaky]

In page 261 of SC guide, we have the following:

Q 2) When he swam across the lake, he struggled to keep his head above the water

SC guide expln-> CORRECT: swam and strugled are both in simple past tense. This is appropriate because the swimming and struggling must have happened at the same time.

My Question:
a) IN SC guide, we have the example - "She played with her friends when the baby sitter arrived". As per expln, 'played' took place after the baby sitter arrived.
As per this expln, 'struggle' should happen after 'swam' in Q2. isn't it?

Please explain.

b) Is this also correct - "When he swam across the lake, he was struggling to keep his head above the water". OR
"When he was swimming across the lake, he struggled to keep his head above the water".

[tim]

a) The babysitter's arrival can be pinpointed to a specific instant of time; swimming across the lake is a process that takes a nonzero amount of time. Thus it makes sense for swim and struggle to happen simultaneously in a way that is precluded by the babysitter example..

b) Both are correct if you change the "when" to "while"..