A neurotransmitter .

a. binds actin filaments, causing them to slide ( p p .2
b. di uses across a synaptic cleft from a neuron to a muscle cell
c. transports ATP across the synaptic cleft
d. breaks down acetylcholine at the synapse

b. di uses across a synaptic cleft from a neuron to a muscle cell.

Explanation:

A neurotransmitter is di uses across a synaptic cleft from a neuron to a muscle cell. Neurotransmitters are chemicals which enable neurotransmission.  In reaction to an impulse a motor neuron axon secretes a neurotransmitter and causes the muscle fiber to contract. It is a chemical messenger which passes on the signals across the chemical synapse.

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answer: b. nucleolus

explanation: nucleolus is a structure in the nucleus are ribosomes are made.

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: d

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: d